A text-book of veterinary anatomy (part 5 of 5)

A text-book of veterinary anatomy (part 5 of 5)

The =dorsal branches= are distributed to the dorso-lateral muscles and skin of the neck. They divide usually into inner and outer branches. The internal branches (Rami mediales) run in general across the multifidus and the lamellar part of the ligamentum nuchæ to the skin of the upper border of the neck; they supply the deep lateral muscles and the skin. The external branches (Rami laterales) are chiefly muscular in their distribution. The dorsal branches of the third to the sixth nerves are connected by anastomotic branches to form the =dorsal cervical plexus=.

The =ventral branches= are smaller than the dorsal ones—an exception to the general rule. They increase in size from first to last. They supply in general the muscles and skin over the lateral and ventral aspect of the vertebræ, but the last three enter into the formation of the brachial plexus, and the three preceding the last give off the roots of the phrenic nerve. An irregular =ventral cervical plexus= is formed by anastomoses established between the ventral branches. The following special features may be noted:

The =first cervical nerve= emerges through the intervertebral (antero-internal) foramen of the atlas. Its =dorsal branch= (N. occipitalis) passes upward and outward between the obliqui capitis and the recti capitis dorsales and supplies branches to these muscles, the scutularis and posterior auricular muscles, and the skin of the poll. The =ventral branch= descends through the alar (antero-external) foramen of the atlas, crosses over the ventral straight muscles and the carotid artery under cover of the parotid gland, and divides into two branches. The anterior branch enters the omo-hyoideus muscle. The posterior branch passes downward and backward under cover of that muscle, unites with a branch of the ventral division of the second cervical nerve, and continues its course on the ventro-lateral surface of the trachea to enter the sterno-thyro-hyoideus behind the intermediate tendon. In the recessus atlantis the ventral branch is connected by one or more twigs with the superior cervical ganglion of the sympathetic, and a little lower with the hypoglossal nerve. It also sends branches to the ventral straight muscles of the head and the thyro-hyoideus. Below the atlas the ventral branch is crossed superficially by the spinal accessory nerve, the occipital artery, and the inferior cerebral vein.

The =second cervical nerve= is larger than the first. It emerges from the vertebral canal through the intervertebral foramen of the anterior part of the arch of the axis. Its =dorsal branch= ascends between the complexus and the ligamentum nuchæ and ramifies in the skin of the poll. The =ventral branch= gives off =muscular branches= to the rectus capitis anterior major, and =anastomotic branches= to the spinal accessory and the ventral divisions of the first and third cervical nerves; one of these crosses over the carotid artery and concurs in the formation of the nerve to the sterno-thyro-hyoideus mentioned above. The ventral branch then becomes superficial by passing between the two parts of the mastoido-humeralis, and divides into posterior auricular and cutaneous branches. The =posterior auricular nerve= passes upward and forward on the parotid gland parallel with the posterior border of the parotido-auricularis to ramify on the convex face of the external ear. The =cutaneous nerve= of the neck (N. cutaneus colli) crosses the mastoido-humeralis muscle and turns backward along the course of the jugular vein. On the lower part of the parotid gland it is connected by a twig with the cervical cutaneous branch of the facial nerve. It gives off twigs to the subcutaneous muscles and the skin of the parotid and laryngeal regions and a long branch which passes forward in the submaxillary space.

The =third cervical nerve= leaves the vertebral canal through the foramen between the second and third cervical vertebræ. Its =dorsal branch= emerges between two bundles of the intertransversalis muscle accompanied by a branch of the vertebral artery, turns upward on the multifidus, and divides into several branches which radiate on the deep face of the complexus. It gives branches to these muscles and to the skin, and a twig which joins the corresponding branch of the fourth nerve. The =ventral branch= emerges through the intertransversalis below the bundle above which the dorsal branch appears. It gives branches to the trachelo-mastoideus, rectus capitis anterior major, longus colli, splenius, and mastoido-humeralis. It also gives off a large cutaneous nerve which passes out between the two parts of the mastoido-humeralis and divides into several divergent branches.

The =fourth= and =fifth cervical nerves= are distributed in general like the third. Their =dorsal branches= are united by anastomotic twigs with each other and with those of the third and sixth nerves to form the dorsal cervical plexus. The =ventral branch= of the fifth nerve often contributes a small twig to the phrenic nerve.

The =sixth cervical nerve= has a smaller =dorsal branch= than the fifth. Its =ventral branch= is larger and goes in part to the brachial plexus; it supplies twigs to the intertransversales, the longus colli, the mastoido-humeralis, and the cervical parts of the serratus and rhomboideus, furnishes a root of the phrenic nerve, and gives off several considerable subcutaneous branches. One of the latter ramifies on the thick part of the cervical panniculus, to which it gives branches; another and larger branch (N. supraclavicularis) sends twigs to the skin over the shoulder joint, and descends to the skin over the superficial pectoral muscles (Fig. 466).

The =seventh= and =eighth cervical nerves= have small =dorsal branches=, which ascend between the longissimus and multifidus, giving twigs to these muscles, the spinalis and semispinalis, the rhomboideus, and the skin. Their =ventral branches= are very large and concur in the formation of the brachial plexus; that of the seventh nerve contributes the posterior root of the phrenic nerve.

PHRENIC NERVE

The =phrenic nerve= (N. phrenicus) (Figs. 428, 429, 433), the motor nerve to the diaphragm, is formed by the union of two or three roots which cross the superficial face of the scalenus muscle obliquely downward and backward. The chief roots come from the ventral branches of the sixth and seventh cervical nerves. The root derived from the fifth nerve is small and inconstant. The root from the seventh cervical comes by way of the brachial plexus. The course of the nerve is not the same on both sides. On the =right side= the nerve enters the thorax by passing between the brachial artery and the anterior vena cava. It then courses backward and somewhat downward over the right face of the anterior vena cava, crosses the pericardium, and continues along the posterior vena cava to the diaphragm. In the latter part of its course it is inclosed in a special fold of the right pleura and inclines gradually to the ventral face of the vein. On the =left side= the nerve enters the thorax between the left brachial and inferior cervical arteries, and then runs its entire course in the mediastinum. In the anterior mediastinum it lies along the brachiocephalic artery ventral to the left vagus and cardiac nerves, and crosses over the dorso-cervical vein. It then passes over the upper part of the pericardium and runs backward in the posterior mediastinum to reach the tendinous center of the diaphragm considerably to the left of the median plane. Each nerve is usually connected near its origin with the first thoracic ganglion of the sympathetic by a ramus communicans, and each terminates by dividing into several branches which are distributed to the corresponding part of the diaphragm.

THE BRACHIAL PLEXUS

The =brachial plexus= (Plexus brachialis) (Fig. 433) results from anastomoses established between the ventral branches of the last three cervical and first two thoracic nerves. It appears as a thick, wide band between the two parts of the scalenus muscle, and is covered by the anterior deep pectoral and subscapularis muscles. The largest root of the plexus is derived from the first thoracic nerve, while the root supplied by the sixth cervical nerve is quite small. Each of the three chief roots, i. e., those from the last two cervical and the first thoracic nerve, is connected with the sympathetic by a ramus communicans.

The =branches= emanating from the plexus go for the most part to the thoracic limb, but some are distributed on the chest-wall. The names of the branches, and their arrangement so far as they can be conveniently examined before removal of the fore limb, are as follows:[207]

1. The large =suprascapular nerve= (N. suprascapularis) turns outward and forward and disappears between the supraspinatus and subscapularis.

2. The much smaller =subscapular nerves= (Nn. subscapulares), usually two primary trunks, arise close behind the suprascapular, run backward a short distance, and divide into several branches which enter the lower third of the subscapularis.

3. The =anterior thoracic= or =pectoral nerves= (N. pectorales craniales), three or four in number, arise from the anterior part of the plexus and from the loop formed by the musculo-cutaneous and median nerves. One enters the anterior deep pectoral muscle. Another passes out between the divisions of the deep pectoral to supply the superficial pectoral, giving a twig usually to the posterior deep muscle. The latter receives one or two other nerves.

4. The =musculo-cutaneous nerve= (N. musculocutaneus) arises from the anterior part of the plexus and passes over the outer face of the brachial artery, below which it is connected by a large but short branch with the median nerve, thus forming a loop in which the artery lies. One or two branches to the pectoral muscles are given off from the nerve or the loop.

5. The =median nerve= (N. medianus) is usually the largest branch of the brachial plexus. It lies at first above the brachial artery, then passes between the artery and vein to reach the anterior border of the former. It is easily recognized by its large size and the loop which it forms with the musculo-cutaneous nerve.

6. The =ulnar nerve= (N. ulnaris) arises with the median by a short common trunk. It descends behind the brachial artery and is accompanied a short distance by the radial nerve.

7. The =radial nerve= (N. radialis) arises from the posterior part of the plexus and is sometimes the largest branch. It descends behind the ulnar nerve over the origin of the subscapular artery and the lower part of the teres major, and dips into the interstice between that muscle and the long and internal heads of the triceps.

8. The =axillary= or =circumflex nerve= (N. axillaris) arises behind the musculo-cutaneous. It passes downward and backward on the inner face of the subscapularis and disappears between that muscle and the subscapular artery.

9. The =long thoracic nerve= (N. thoracalis longus) is wide and thin. It passes backward across the surface of the serratus magnus, to which it is distributed. The branches which enter the muscle are given off both upward and downward in fairly regular fashion.

10. The =thoraco-dorsal nerve= (N. thoracodorsalis) passes upward and backward across the subscapularis muscle to ramify in the teres major and the latissimus dorsi.

11. The =external= (or subcutaneous) =thoracic nerve= arises by a common trunk with the ulnar. It runs backward and downward across the inner face of the tensor fasciæ antibrachii, communicates with the anterior pectoral branches, and gives twigs to the deep pectoral muscle. It then runs backward in company with the external thoracic or “spur” vein, gives branches to the latissimus dorsi and the deep pectoral, and ramifies in the panniculus and the skin of the abdominal wall. It communicates with perforating branches of the intercostal nerves. A branch from it, accompanied by a large perforating intercostal branch, winds around the lower border of the latissimus dorsi and ramifies in the panniculus on the outer surface of the arm.

The term posterior thoracic or pectoral nerves (Nn. pectorales caudales) may be used to include 8, 9, and 10.

SUPRASCAPULAR NERVE

The =suprascapular= (Fig. 441) is a large nerve derived chiefly, if not exclusively, from the sixth and seventh cervical components of the brachial plexus. It passes between the supraspinatus and subscapularis muscles and turns around the distal fourth of the anterior border of the scapula to reach the supraspinous fossa. It gives branches to the supraspinatus and continues backward and upward into the infraspinous fossa, where it supplies the infraspinatus, deltoid, and teres minor muscles.

The direct relation of this nerve to the scapula renders it liable to injury, the result of which may be paralysis and atrophy of the muscles supplied by it.

MUSCULO-CUTANEOUS NERVE

The =musculo-cutaneous nerve= (Fig. 441) arises close behind the suprascapular, and is derived chiefly from the part of the brachial plexus which is supplied by the seventh and eighth cervical nerves. It descends across the outer surface of the brachial artery, below which a great part of the nerve unites with the median to form the loop previously mentioned. It gives off a branch which enters the upper part of the belly of the coraco-brachialis, passes downward and forward between the two parts of that muscle or between the muscle and the bone, and divides into branches which enter the biceps brachii. It contributes one of the nerves to the pectoral muscles. In some cases this nerve sends a branch to join the cutaneous branch of the median.

AXILLARY NERVE

The =axillary nerve= (Figs. 441, 520), also termed the circumflex, derives its fibers from the eighth cervical and first thoracic roots of the brachial plexus. It runs downward and backward across the lower part of the subscapularis and dips in between that muscle and the subscapular artery at the level of the shoulder joint. Continuing outward in the interval between the teres minor and the long and external heads of the triceps, it reaches the deep face of the deltoid and divides into several divergent branches. The =muscular branches= supply the teres major, capsularis, teres minor, infraspinatus, deltoid, and mastoido-humeralis. The =cutaneous branch= (N. cutaneus brachii lateralis) runs downward and a little forward across the external head of the triceps and ramifies on the fascia on the front of the forearm and on the superficial pectoral muscle.

RADIAL NERVE

The =radial nerve= (Figs. 441, 443, 520), also called the musculo-spiral, is sometimes the largest branch of the brachial plexus. Its fibers are derived from the seventh and eighth cervical and first thoracic roots of the plexus. It passes downward and backward over the inner surface of the subscapular artery and the teres major. In this part of its course it is related in front to the ulnar nerve, which separates it from the brachial vein. It detaches a branch to the tensor fasciæ antibrachii, passes outward in the interval between the teres major and the long and internal heads of the triceps, and gains the musculo-spiral groove of the humerus. Accompanied by a branch of the deep brachial artery, it runs obliquely downward and outward in the groove, covered externally by the external head of the triceps and the extensor carpi radialis, and reaches the flexion surface of the elbow joint. In this part of its course it gives off a muscular branch which ramifies in the long and external heads of the triceps and in the anconeus, and a =cutaneous nerve= (N. cutaneus antibrachii dorsalis); branches of the latter emerge below or through the external head of the triceps and ramify on the dorso-lateral surface of the forearm. At the elbow the nerve descends with the anterior radial vessels on the joint capsule between the brachialis and extensor carpi radialis, and supplies branches to the extensor carpi and the common or anterior extensor of the digit and (inconstantly) to the brachialis. Below the elbow joint the nerve detaches a large branch which passes back to the flexor carpi externus, and terminates by small branches which descend on the radius to enter the radial and ulnar heads of the common extensor, the lateral extensor, and the oblique extensor of the carpus. Thus the radial nerve innervates the extensors of the elbow, carpal and digital joints, and supplies also the flexor carpi externus.[208]

ULNAR NERVE

The =ulnar nerve= (Figs. 441, 442, 443, 520) arises with the median from the thoracic components of the brachial plexus. It descends between the brachial artery and vein, accompanied for a short distance by the radial nerve. It then crosses the vein and continues behind the latter along the anterior border of the tensor fasciæ antibrachii and dips under that muscle near the elbow. Here it is joined by the ulnar vessels and passes downward and backward over the internal epicondyle of the humerus. In the forearm it crosses obliquely the deep face of the ulnar head of the flexor carpi medius and descends under the deep fascia with the vessels, at first on the ulnar head of the perforans, and then between the middle and external flexors of the carpus. Near the level of the accessory carpal bone it divides into two terminal branches, superficial and deep. It gives off two principal collateral branches. The =cutaneous branch= (Ramus cutaneus palmaris) is detached just before the nerve passes under the tensor fasciæ antibrachii; it runs downward and backward on that muscle under cover of the posterior superficial pectoral, becomes superficial below the elbow and ramifies on the posterior surface and both sides of the forearm. The =muscular branch= is given off at the elbow joint and divides to supply the flexors of the digit and the middle flexor of the carpus. Of the two terminals, the =superficial branch= (Ramus superficialis) emerges between the tendons of insertion of the external and middle flexors of the carpus and ramifies on the dorso-lateral aspect of the carpus and metacarpus. The =deep branch= (Ramus profundus), after a very short course, unites under cover of the tendon of the flexor carpi medius with the outer branch of the median nerve to form the external metacarpal or volar nerve.

MEDIAN NERVE

The =median nerve= (Figs. 441, 442, 447, 520, 521) derives its fibers chiefly from the first thoracic root of the brachial plexus. It is usually the largest branch and it accompanies the chief arterial trunks to the distal part of the limb. It descends over the inner face of the brachial artery, which it crosses obliquely, and continues down the arm in front of the artery. Near its origin it is joined by a large branch with the musculo-cutaneous nerve, thus forming a loop in which the artery appears to be suspended. Near the elbow it crosses obliquely over the artery (posterior radial) and lies behind it on the internal lateral ligament. Below the joint it again crosses the artery and lies behind the radius and the lower part of the long internal lateral ligament.

At the elbow the nerve is covered by the posterior superficial pectoral muscle and is crossed by the large oblique connection between the cephalic and brachial veins. The variable and often plexiform venous arrangement renders approach to the nerve here undesirable. It can be reached best by an incision just behind the lower part of the long internal lateral ligament; here the nerve lies under the deep fascia in the furrow between the radius and the anterior border of the flexor carpi internus, overlapped by the latter. In some cases the nerve retains its position in front of the artery at the elbow, and in others it crosses the deep face of the artery.

Passing beneath the internal flexor of the carpus, the nerve continues downward in the forearm with the posterior radial vessels, and divides at a variable distance above the carpus into two branches; these are the internal volar or metacarpal nerve and the branch which unites with the ulnar to form the corresponding external nerve.

At the proximal part of the forearm the nerve runs almost straight downward along the posterior border of the long internal lateral ligament, while the artery here inclines somewhat backward. Thus the nerve is superficial to the artery for a short distance, then lies in front of the latter to about the middle of the region, where it inclines a little backward and arrives at the interval between the internal and middle flexors of the carpus. The division may occur about the middle of the region, but commonly takes place in the distal third or fourth.

The collateral branches are as follows:

1. The =musculo-cutaneous branch= is in reality the continuation of the nerve of that name. It is given off about the middle of the arm, passes beneath the lower part of the biceps, and divides into muscular and cutaneous branches. The =muscular branch= enters the brachialis. The =cutaneous branch= emerges between the mastoido-humeralis and the biceps and divides into two branches; these descend on the fascia of the forearm with the cephalic vein and its accessory, and ramify on the front and inner face of the forearm, carpus, and metacarpus.

2. =Muscular branches= to the internal flexor of the carpus and the flexors of the digit are given off just as the nerve passes under the first named muscle.

3. The very small =interosseous nerve= passes through the interosseous space and is distributed chiefly to the periosteum, but in some cases twigs may go to the extensor muscles.

The =metacarpal= or =volar nerves=,[209] internal and external, are the continuations of the median and ulnar nerves in the distal part of the limb.

The =internal metacarpal= or =volar nerve= (N. volaris medialis) arises as the inner terminal branch of the median nerve at a variable distance above the carpus (Fig. 442). It descends through the carpal canal along the inner border of the superficial flexor tendon, and lies at first in front of the large metacarpal or common digital artery. It then passes behind the artery to the distal third of the metacarpus, where it lies behind the vein, the artery here becoming deeper in position. In addition to cutaneous twigs, the nerve gives off about the middle of the metacarpus a considerable =anastomotic branch= which winds obliquely downward and outward over the flexor tendons and joins the external nerve at the lower third of the metacarpus (Fig. 447). Near the fetlock the nerve divides into two digital branches.

1. The =dorsal= or =anterior digital branch= (Ramus dorsalis) descends at first between the digital artery and vein, then crosses over the vein and ramifies in the skin and the matrix of the hoof on the dorsal (anterior) face of the digit.

2. The =volar= or =posterior digital branch= (Ramus volaris) is the direct continuation of the trunk. It descends behind the digital artery, which it accompanies in its ramification. A =middle digital branch= is sometimes described as descending behind the vein. In some cases this branch is distinct, but usually there are instead several small twigs derived from the posterior branch, which cross very obliquely over the artery and anastomose in a variable manner with each other and with the anterior branch.

The =external metacarpal= or =velar nerve= (N. volaris lateralis) is formed by the union of the external terminal branch of the median with the deep branch of the ulnar nerve (Fig. 442). It descends with the internal volar or small metacarpal artery in the texture of the posterior annular ligament of the carpus. In the metacarpus it descends along the outer border of the deep flexor tendon behind the external metacarpal vein, and is accompanied by a small artery from the volar subcarpal arch. Toward the distal end of the metacarpus it is joined by the oblique branch from the internal nerve, and beyond this is arranged like the latter. Below the carpus it detaches a deep branch to the suspensory ligament and the interossei, and also supplies twigs to the skin.

Anastomoses are established between the digital branches, and the areas innervated by them are not well defined, but really overlap each other. In certain diseased conditions, however, in which the lesions are confined to the volar structures, relief from pain may be afforded by section of the volar branches only.

THE THORACIC NERVES

The =thoracic nerves= (Nn. thoracales) number eighteen on either side in the horse. They are designated numerically according to the vertebræ behind which they emerge. Most of them are arranged in a very similar manner and therefore do not require separate description. Each divides into a dorsal and a ventral branch, the latter being the larger.

The =dorsal branches= (Rami dorsales) emerge behind the levatores costarum and divide into internal and external branches. The internal branches ascend on the multifidus and supply the dorsal spinal muscles. The external branches run outward under the longissimus and emerge between that muscle and the transversalis costarum; after giving twigs to these muscles they pass through the latissimus dorsi and the lumbo-dorsal fascia and ramify as dorsal cutaneous nerves under the skin of the back (Fig. 523). In the region of the withers they give branches to the serratus anticus and rhomboideus, and their cutaneous terminals pass through these muscles and the dorso-scapular ligament to supply the skin over the ligamentum nuchæ and the scapular cartilage.

The =ventral branches= or =intercostal nerves= (Nn. intercostales) are much larger than the preceding, and are connected with the sympathetic by rami communicantes. The first goes almost entirely to the brachial plexus, but sends a fine branch downward in the first intercostal space which is expended in the muscle there without reaching the lower end of the space. The second ventral branch furnishes a considerable root to the brachial plexus, but its intercostal continuation is typical. The intercostal nerves (Fig. 184) descend in the intercostal spaces with the vessels of like name, at first between the intercostal muscles, and lower down chiefly between the pleura and the internal intercostal muscle. In the anterior spaces the artery lies along the posterior border of the rib, with the nerve in front of it; further back the nerve lies behind the border of the rib, with the artery in front of it. They supply the intercostal muscles, give off lateral perforating branches, and terminate in the following manner: The second to the sixth inclusive emerge through the spaces between the costal cartilages and concur in supplying the pectoral muscles. The second to the eighth give branches to the transversus thoracis. The succeeding ones give branches to the diaphragm, pass between the transverse and internal oblique muscles, give twigs to these, and end in the rectus abdominis. There are three series of cutaneous nerves given off by the intercostal nerves. The upper nerves emerge through the serratus magnus and the external intercostals about parallel with the digitations of the external oblique. The middle set perforate the origin of the latter muscle. The lower ones appear through the abdominal tunic. They supply branches to the abdominal muscles, the panniculus, and the skin. Some of the anterior ones anastomose with the posterior thoracic branches of the brachial plexus. The posterior three supply in part the skin of the flank. The ventral branch of the last thoracic nerve runs outward behind the last rib across the dorsal surface of the psoas major and divides into superficial and deep branches. The superficial branch passes between the obliquus internus and transversus abdominis, perforates the obliquus externus, and ramifies under the skin of the flank (Fig. 525). The deep branch descends on the inner face of the internal oblique to the rectus abdominis, in which it ends.

THE LUMBAR NERVES

There are six pairs of =lumbar nerves= (Nn. lumbales) in the horse, the last of which emerge between the last lumbar vertebra and the sacrum. The anterior two or three are about the same size as the thoracic nerves, but the others are much larger.

Their =dorsal branches= are small in comparison with the ventral ones. They are distributed to the muscles and skin of the loins and croup in a fashion similar to those of the thoracic nerves.

The =ventral branches= are connected with the sympathetic by small rami communicantes, and give branches to the sublumbar muscles. Those of the first two nerves are arranged in a manner analogous to the corresponding branch of the last thoracic nerve.

The ventral branch of the =first lumbar nerve= is termed the =ilio-hypogastric nerve= (N. iliohypogastricus). It passes outward between the quadratus lumborum and the psoas major, and divides at the outer border of the latter into an anterior or superficial and a posterior or deep branch. The =anterior= or =superficial branch= passes over the upper edge of the internal oblique, descends between that muscle and the external oblique, perforates the latter, and runs downward and backward and ramifies under the skin of the posterior part of the flank and the outer surface of the thigh. It gives branches to the transversus and obliquus externus abdominis. The =posterior= or =deep branch= is smaller; it runs downward and backward beneath the peritoneum to the outer border of the rectus abdominis, gives branches to the internal oblique, and terminates in the rectus abdominis.

The ventral branch of the =second lumbar nerve= is connected by an anastomotic branch with that of the third nerve. It gives off a large branch to the psoas muscle and an inguinal branch, and is continued as the ilio-inguinal nerve. The =inguinal branch= (N. spermaticus externus) runs backward in the substance of the psoas minor, emerges a short distance in front of the circumflex iliac vessels, and runs backward and downward under the peritoneum to the internal inguinal ring. It gives branches to the internal oblique muscle and descends in the inguinal canal along the outer border of the cremaster (to which it detaches filaments) and ends subcutaneously in the scrotum and prepuce in the male, the mammary gland in the female. The =ilio-inguinal nerve= (N. ilioinguinalis) may be regarded as the continuation of the ventral branch. It runs parallel with the ilio-hypogastric nerve and has a similar arrangement. Its =anterior= or =superficial branch= perforates the external oblique muscle a little in front of the point of the hip, runs downward on the front of the thigh and the outer surface of the stifle, and gives off cutaneous branches. The =posterior= or =deep branch= runs behind and parallel with that of the iliohypogastricus, detaches branches to the internal oblique muscle, and descends the inguinal canal with the inguinal branch, to be distributed to the external genital organs and the surrounding skin in the inguinal region.

The ventral branch of the =third lumbar nerve= is connected by a small anastomotic branch with the second nerve and furnishes a root of the lumbo-sacral plexus. It gives off a branch to the psoas muscles, an inguinal branch, and is continued as the external cutaneous nerve. The =inguinal branch= (N. spermaticus externus) passes backward in the substance of the psoas minor, from which it emerges under cover of or near the circumflex iliac vessels. It then runs external to and parallel with the external iliac artery and descends in the inner part of the inguinal canal. It emerges at the external ring with the external pudic artery and ramifies in the external genital organs and the skin of the inguinal region. The =external cutaneous nerve= of the thigh (N. cutaneus femoris lateralis) runs backward in the substance of the psoas muscles and emerges at the outer border of the psoas minor. It then passes outward and backward on the iliac fascia and accompanies the posterior branch of the circumflex iliac artery. With this vessel it perforates the abdominal wall by passing between the external oblique and the iliacus a short distance below the point of the hip, and descends on the inner face of the tensor fasciæ latæ (near its anterior border) and ramifies subcutaneously in the region of the stifle.

The origin and disposition of some of the foregoing nerves are variable. In some cases the ilio-inguinal nerve ends in the psoas major, and appears then to be absent. The mode of formation of the inguinal nerves is very inconstant. The inner nerve may arise with one of the outer ones from a common trunk, or they may anastomose. The inguinal branch of the ilio-inguinal nerve often receives a twig from the ilio-hypogastric nerve.

The ventral branches of the =fourth=, =fifth=, and =sixth lumbar= nerves concur in the formation of the lumbo-sacral plexus.

LUMBO-SACRAL PLEXUS

This plexus (Fig. 451) results substantially from the union of the ventral branches of the last three lumbar and the first two sacral nerves, but it derives a small root from the third lumbar nerve also. The anterior part of the plexus lies in front of the internal iliac artery between the lumbar transverse processes and the psoas minor. The posterior part lies partly upon and partly in the texture of the sacro-sciatic ligament. From the plexus are derived the nerves of the pelvic limb, which are now to be described.

FEMORAL NERVE

The =femoral= (or anterior crural) nerve (N. femoralis) is derived chiefly from the fourth and fifth lumbar nerves, but commonly receives a fasciculus from the third nerve also (Fig. 524). It is the larger of the two nerves which are given off from the anterior part of the lumbo-sacral plexus. It runs backward at first between the psoas major and minor, then crosses the deep face of the tendon of insertion of the latter, and descends under cover of the sartorius in the furrow between the two heads of the iliacus. It gives off the saphenous nerve, crosses the lower part of the outer head of the iliacus, and divides into several branches which dip into the interstice between the rectus femoris and the vastus internus (Fig. 450). These branches are accompanied by the anterior femoral vessels and innervate the quadriceps femoris. Collateral muscular branches are supplied to the ilio-psoas and sartorius.

The =saphenous nerve= (N. saphenus) (Figs. 450, 451, 457) is given off as the parent trunk crosses the furrow between the psoas major and the outer head of the iliacus. It descends with the femoral vessels in the femoral canal, and gives branches to the sartorius, gracilis, and pectineus. About the middle of the thigh it divides into several branches which emerge from between the sartorius and gracilis, perforate the deep fascia and ramify on the inner surface and the front of the limb as far downward as the hock. The longer posterior branches accompany the saphenous vessels, while the anterior branches deviate forward toward the stifle and the anterior surface of the leg.

OBTURATOR NERVE

This nerve (N. obturatorius) is derived from the ventral branches of the last three lumbar nerves (Fig. 524). It runs downward and backward, at first above and then upon the external iliac vein, inclines inward across the obturator vein, and passes through the anterior part of the obturator foramen in front of that vessel (Fig. 451). It continues downward through the obturator externus, and divides into several branches which innervate the obturator externus, pectineus, adductor, and gracilis muscles (Fig. 456).

ANTERIOR GLUTEAL NERVE

This nerve (N. glutæus cranialis) is derived chiefly from the last lumbar and first sacral nerves. It divides into four or five branches which emerge through the great sacro-sciatic foramen with the divisions of the anterior gluteal artery and supply the gluteal and tensor fasciæ latæ muscles. The nerve to the latter and the anterior part of the superficial gluteus passes between the deep part of the gluteus medius and the deep gluteal muscle, and is accompanied on the iliacus by branches of the external circumflex vessels.

POSTERIOR GLUTEAL NERVE

The =posterior gluteal nerve= (N. glutæus caudalis) is derived mainly from the sacral roots of the lumbo-sacral plexus (Figs. 451, 526). It divides into two trunks which emerge above the great sciatic nerve. The upper nerve passes backward on the sacro-sciatic ligament and divides into branches which enter the two heads of the biceps femoris; it supplies a branch to the posterior part of the middle gluteus, and a nerve which turns around the posterior border of the latter and enters the posterior head of the superficial gluteus. The inferior nerve runs downward and backward on the sacro-sciatic ligament and divides into the =posterior cutaneous nerve= and muscular branches which supply the semitendinosus. The former (N. cutaneus femoris caudalis) passes through the biceps femoris, emerges between that muscle and the semitendinosus a little below the level of the tuber ischii, and ramifies subcutaneously on the outer and posterior surfaces of the hip and thigh (Fig. 525).

GREAT SCIATIC NERVE

The =great sciatic nerve= (N. ischiadicus) (Figs. 451, 455, 526), the largest in the body, is derived chiefly from the last lumbar and the sacral roots of the lumbo-sacral plexus, but may receive a fasciculus from the third sacral nerve also. It emerges through the great sacro-sciatic foramen as a broad flat band—blended at first with the posterior gluteal nerve—which passes downward and backward on the lower part of the sacro-sciatic ligament and on the origin of the deep gluteus muscle. It turns downward in the hollow between the trochanter major and the tuber ischii over the gemellus, the tendon of the obturator internus, and the quadratus femoris. In its descent in the thigh it lies between the biceps femoris externally and the adductor, semimembranosus, and semitendinosus internally, and it is continued between the two heads of the gastrocnemius as the tibial nerve. Its chief branches are as follows:

1. In the pelvic part of its course the sciatic nerve supplies small branches to the obturator internus, gemellus, and quadratus femoris; the branch to the obturator internus reaches the muscle by passing through the anterior end of the lesser sacro-sciatic foramen.

2. As the sciatic nerve turns down behind the hip joint it gives off a large branch (Ramus muscularis proximalis) which divides to supply the semimembranosus and the short heads of the biceps femoris and semitendinosus.

3. The =posterior cutaneous nerve= of the leg or =external saphenous nerve= (N. cutaneus suræ posterior) is detached from the sciatic about the middle of the thigh. It receives a fasciculus from the peroneal nerve and descends with the recurrent tarsal vein on the outer face of the gastrocnemius to the distal third of the leg. Here it perforates the deep fascia and ramifies under the skin on the outer surface of the tarsus and metatarsus (Fig. 525).

4. The =peroneal= or =external popliteal nerve= (N. peronæus) (Figs. 455, 460, 527) is a large trunk which arises from the great sciatic nerve very shortly after the latter emerges from the pelvic cavity. It descends with the parent trunk to the origin of the gastrocnemius; here the peroneal nerve deviates outward and forward across the external face of the gastrocnemius under cover of the biceps femoris, and divides at the origin of the lateral extensor muscle into superficial and deep branches. The collateral branches include a twig to the biceps femoris, the reinforcing fasciculus detached about the middle of the thigh to the posterior cutaneous nerve, and, lower down, the =external cutaneous nerve= of the leg (Ramus cutaneus suræ lateralis). The latter, also known as the peroneal cutaneous nerve, emerges between the middle and posterior divisions of the biceps femoris at the level of the stifle joint and ramifies under the skin. The =superficial peroneal= or =musculo-cutaneous nerve= (N. peronæus superficialis) furnishes branches to the lateral extensor, and descends in the furrow between that muscle and the anterior extensor, perforates the deep fascia of the leg, and ramifies under the skin on the front and the outer face of the tarsus and metatarsus. The =deep peroneal= or =anterior tibial nerve= (N. peronæus profundus) is the direct continuation in point of size of the peroneal trunk. It dips in between the lateral and anterior extensors of the digit, gives branches to these muscles and the tibialis anterior, and descends in front of the intermuscular septum which separates the former. It continues downward behind the tendon of the anterior extensor and divides on the front of the hock into internal and external branches. The =internal branch= (Ramus medialis) passes down under the skin on the anterior face of the metatarsus and supplies the cutaneous fibers of this region. The =external branch= (Ramus lateralis) furnishes a twig to the extensor brevis muscle and descends with the great metatarsal artery. It supplies the skin on the outer face of the metatarsus and the fetlock.

In the greater part of its course in the leg the deep peroneal nerve is separated from the anterior tibial vessels by the tibialis anterior (muscular part of the flexor metatarsi). It should be noted that the outer of the two veins which almost always accompany the artery here is frequently very large, and the layer of muscle which intervenes between it and the nerve is often exceedingly thin. In the distal part of the leg the nerve is in direct contact with the vein, and on the front of the hock it lies behind the vessels.

TIBIAL NERVE

The =tibial nerve= (N. tibialis), also termed the posterior tibial, is the direct continuation of the great sciatic nerve (Figs. 451, 455, 458, 459, 527). It passes down between the two heads of the gastrocnemius, and accompanies the recurrent tibial vessels to the distal third of the leg, where it divides into internal and external plantar nerves. In the upper third of the leg it lies along the inner side of the superficial flexor under cover of the internal head of the gastrocnemius; lower down it is covered by the common deep fascia and is situated in the space between the deep flexor and the inner border of the tendo Achillis.

At the usual point of election for tibial neurectomy, i. e., about a handbreadth above the level of the tuber calcis, the nerve lies in areolar tissue and fat in a fascial compartment formed by the special fascia of the deep flexor in front and by the common fascia and the accessory or tarsal tendon of the semitendinosus and biceps femoris behind and internally.

At its origin the tibial nerve gives off a =muscular branch= (Ramus muscularis distalis), the divisions of which pass between the two heads of the gastrocnemius and radiate to supply that muscle, the popliteus, the soleus, and the flexors of the digit. Small cutaneous twigs are also detached along the course of the nerve.

PLANTAR NERVES

The =plantar nerves=, internal and external (N. plantaris medialis, lateralis), result from the bifurcation of the tibial nerve in the lower part of the leg (Figs. 458, 459). They continue at first in the same direction and relations as the parent trunk, in direct apposition and inclosed in a common sheath. At the hock they diverge at a very acute angle and descend in the tarsal canal behind the deep flexor tendon in company with the plantar arteries. The internal plantar nerve supplies cutaneous nerves to the inner aspect of the tarsus and metatarsus, descends along the inner border of the flexor tendons behind the superficial plantar metatarsal vessels, and is otherwise arranged like the corresponding volar nerve of the fore limb. The external plantar nerve deviates outward between the two flexor tendons to reach their outer border. It supplies a branch to the suspensory ligament, and in its further course resembles the corresponding nerve of the fore limb.

In so-called “tibial” neurectomy the operator really cuts the two plantar nerves which have not yet separated. The anastomotic branch between the two plantar nerves is smaller than that which connects the corresponding nerves of the fore limb, and is absent in 30 per cent. of the cases, according to Rudert.

SACRAL NERVES

Five pairs of =sacral nerves= (Nn. sacrales) are present in the horse.

The small =dorsal branches= emerge through the dorsal sacral foramina and the space between the sacrum and the first coccygeal vertebra, and ramify in the muscles and skin of the sacral region and the adjacent part of the tail (Fig. 525). The fifth anastomoses with the dorsal branch of the first coccygeal nerve.

The =ventral branches= leave the vertebral canal through the ventral sacral foramina and the interval between the sacrum and first coccygeal vertebra. They are connected with the sympathetic by rami communicantes, and contribute branches to the pelvic plexus. The first and second are the largest, and unite with each other and with those of the last three lumbar nerves to form the lumbo-sacral plexus. The third and fourth are connected with each other, and the majority of their fibers go to form the pudic and posterior hæmorrhoidal nerves.

The =pudic nerve= (N. pudendus) (Figs. 451, 455, 526) accompanies the internal pudic artery to the ischial arch, turns around the latter, parting company with the artery, and pursues a flexuous course along the dorsum penis as the =nervus dorsalis penis= and ramifies in the glans and the penile layer of the prepuce. Within the pelvis it anastomoses with the posterior hæmorrhoidal nerve, and gives branches to the bladder and urethra, the terminal part of the rectum, and the skin and muscles of the anus (Fig. 452). It also supplies the nerve to the ischio-cavernosus muscle and numerous branches to the corpus cavernosum and corpus spongiosum. In the female it terminates in the clitoris and vulva (Fig. 453).

The =posterior hæmorrhoidal nerve= (N. hæmorrhoidalis caudalis) passes downward and backward above the pudic nerve, with which it anastomoses. It gives twigs to the terminal part of the rectum, the sphincter ani externus, and the surrounding skin (Fig. 452). In the female it supplies twigs to the vulva also (Fig. 453).

The ventral branch of the fifth nerve is small. It gives twigs to the sacro-coccygeus ventralis lateralis and the skin of the root of the tail and joins the first coccygeal nerve.

COCCYGEAL NERVES

The =coccygeal nerves= (Nn. coccygei) commonly number five pairs. Their dorsal and ventral branches anastomose to form respectively two trunks on either side, which extend to the tip of the tail and supply its muscular and cutaneous nerves. The dorsal trunk runs with the dorso-lateral artery between the sacro-coccygeus dorsalis and intertransversales muscles (Fig. 454). The ventral trunk accompanies the ventro-lateral artery below the intertransversales.

THE SYMPATHETIC NERVOUS SYSTEM[210]

The =sympathetic nervous system= (Systema nervorum sympathicum) is that part of the nervous system which serves (1) to transmit stimuli to the heart-muscle, unstriped muscle, and glands; (2) to conduct impulses from the viscera to the cerebrospinal system.

Many of the fibers are derived from the cerebrospinal system and are rearranged and distributed in the sympathetic system. Numerous sympathetic fibers are contributed to the cerebrospinal nerves, through which they are distributed to the unstriped muscular tissue and glands, as vasomotor, pilomotor, and secretory nerves. The sympathetic, like the cerebrospinal system, consists of neurones, each of which comprises the cell-body, an axone, and numerous branched dendrites. The cell-bodies are aggregated into =ganglia=, some of which are large and more or less constant in position and form, while others are microscopic; and are scattered in an irregular manner through the peripheral part of the system. It is probable that simple visceral reflexes may be mediated by sympathetic neurones alone.

In descriptive anatomy the sympathetic system is regarded as consisting of (1) a chain of =ganglia= extending along either side of the vertebral column and connected by association fibers to form the =sympathetic trunk=; (2) =central branches= to and from the cerebrospinal nerves; (3) =peripheral branches=, which form =plexuses= with each other and the cerebrospinal nerves; (4) the =peripheral ganglia= which are interposed in the plexuses.

The =sympathetic trunk= (Truncus sympathicus) extends on either side from the base of the cranium to the tail. In it are interposed, at intervals of varying regularity, the =ganglia of the sympathetic trunk= (Ganglia trunci sympathici). These are connected with the cerebrospinal nerves by central branches, the =rami communicantes=.

Two kinds of rami communicantes occur. Of these, one type consists largely of medullated fibers derived from the spinal nerves and ganglia; they have therefore a white appearance, and are termed =white rami=. They contain both efferent and afferent fibers. The =efferent splanchnic fibers= are derived from the ventral roots of the spinal nerves and terminate in great part about the cells of the nearest sympathetic ganglion; others end in more distant or in peripheral ganglia. The =afferent splanchnic fibers= are chiefly peripheral processes of the cells of the spinal ganglia, but some are sympathetic fibers which enter the spinal nerve-trunk and terminate about cells of the spinal ganglion. The =gray rami= consist mainly of non-medullated fibers derived from the sympathetic ganglia directly or through the trunk, which proceed centrally to the spinal nerves and are distributed along the somatic divisions of the latter to unstriped muscle and glands as =vasomotor=, =pilomotor=, and =secretory fibers=. Some go to the membranes of the spinal cord, and a few terminate about cells of the spinal ganglia as sensory sympathetic fibers.

Similar but more complex and irregular communications which exist between the sympathetic system and the cranial nerves—with the exception of the first and second—have been referred to in the accounts of the latter.

It is convenient for descriptive purposes to divide the sympathetic system into cephalic, cervical, thoracic, abdominal, and pelvic parts.

1. The =cephalic part= (Pars cephalica systematis sympathici) comprises the =otic=, =sphenopalatine=, and =ciliary ganglia=, which may be regarded as homologues of the ganglia of the trunk of other regions. It also includes three plexuses formed by branches derived from the superior cervical ganglion. The ganglion gives off two or three filaments which subdivide to form the =internal carotid plexus= around the artery of like name. The =cavernous plexus= surrounds the artery within the cavernous sinus and communicates with that of the opposite side. The =external carotid plexus= is formed around the homonymous artery, and filaments from it go to the vessel and its branches and to the salivary glands.

2. The =cervical part= (Pars cervicalis s. sympathici) includes two ganglia and the trunk which connects them.

The =superior= or =anterior cervical ganglion= (G. cervicale craniale) lies on the guttural pouch below the occipito-atlantal articulation (Fig. 437). It is reddish-gray in color, fusiform, and about an inch (ca. 2 to 3 cm.) in length. It is connected by rami communicantes with the last four cranial and first cervical nerves, sends branches to form the plexuses mentioned above, and contributes to the pharyngeal plexus.

The =cervical trunk= of the sympathetic connects the superior and inferior cervical ganglia. On leaving the former it is associated in a common sheath with the vagus along the dorsal face of the common carotid artery. At the root of the neck it separates from the vagus and joins the inferior ganglion.

The =inferior= or =posterior cervical ganglion= (G. cervicale caudale) is situated under the first rib and the insertion of the scalenus (Figs. 428, 429). On the right side it lies upon the longus colli and the trachea, on the left side upon the same muscle and the œsophagus. It is flattened, very irregular and variable in outline, and is blended more or less with the first thoracic ganglion. It is connected by large gray rami with the ventral branches of the last two cervical nerves, and by small filaments with the recurrent nerve. It receives a nerve—termed by Schmaltz the nervus transversarius—which accompanies the vertebral artery; through it rami come from the second to the sixth cervical nerves inclusive.

A =middle cervical ganglion= may be present, and occurs oftenest on the right side. It lies on the carotid artery an inch or two in front of the first rib and is intercalated in the vago-sympathetic trunk.

The =cardiac nerves= (Nn. cardiaci) are formed by branches from the inferior cervical and first thoracic ganglia, together with twigs from the sympathetic trunks and the vagi. They form a plexus (P. cardiacus) on the ventral face of the trachea with each other and with branches of the vagus and recurrent nerves. They are subject to considerable variation, but their general arrangement may be stated as follows:

(a) On the right side there are usually two cardiac nerves. Of these one passes back with the vagus in the angle between the right brachial artery and the common carotid trunk, pierces the pericardium, crosses the aortic arch, and divides into branches which are mingled with those of the left nerves. The second crosses obliquely over the right face of the trachea and joins the vagus, where the latter gives off the right recurrent nerve; a small plexus is formed here, from which two or three cardiac branches are detached. These pass back beneath the trachea and ramify on the atria and ventricles.

(b) On the left side there are commonly three cardiac nerves. One of these is distributed to the great vessels in the anterior mediastinum. The largest passes back at first with the vagus beneath the arch of the left brachial artery, inclines downward, perforates the pericardium, and divides into two branches. One branch passes beneath the bifurcation of the pulmonary artery and is distributed to the left atrium. The larger branch dips in between the aorta and the pulmonary artery, gives twigs to these vessels, and ramifies on the ventricles, especially along the course of the right coronary artery. The third nerve crosses the deep face of the left brachial artery, passes back below the trachea, and unites with filaments of a right cardiac nerve. It passes around the aorta and ramifies chiefly along the course of the left coronary artery on the left face of the ventricles.

3. The =thoracic part= (Pars thoracalis systematis sympathici) extends below the costo-vertebral joints from the inferior cervical ganglion to the upper border of the diaphragm, and passes between the latter and the psoas minor to be continued by the abdominal part.

The =trunk= is concealed in the first part of its course by the outer border of the longus colli, but further back it is visible under the pleura.

The =ganglia= are arranged segmentally at each intercostal space and partly on the heads of the ribs. They are flattened and are small and fusiform, with the exception of the first. This (G. thoracale primum) is extensive, irregularly quadrilateral in outline, and is united with the inferior cervical ganglion. The ganglia are connected with the thoracic nerves by white and gray rami communicantes.

The =visceral branches= comprise aortic, cardiac, pulmonary, and œsophageal branches, and the splanchnic nerves. The =aortic branches= ramify on the thoracic artery, forming around that vessel the =thoracic aortic plexus= (P. aorticus thoracalis). The =cardiac branches= concur with those of the vagus in forming the =cardiac plexus= (P. cardiacus). From this branches go to form the =coronary plexuses= (P. coronarii) along the course of the vessels of like name. The =pulmonary branches= join with corresponding branches of the vagus and filaments from the cardiac plexus in forming the =pulmonary plexus= (P. pulmonalis) at the root of the lung. Branches of the plexus, on which are minute ganglia, ramify with the bronchi in the substance of the lung.[211] The =œsophageal branches= join with those of the vagus in the formation of the =œsophageal plexus= (P. œsophageus).

The =great splanchnic nerve= (N. splanchnicus major) arises by a series of roots derived from the sixth or seventh to the fifteenth or sixteenth thoracic ganglia inclusive. It extends at first along the inner side of the thoracic trunk, then crosses the latter ventrally, passes back between the crus of the diaphragm and the outer border of the psoas minor, and joins the cœliac ganglion. It is small at its origin, but becomes considerably larger than the sympathetic trunk. Near its termination it bears the small =splanchnic ganglion=, from which and from the nerve, filaments go to the aorta, the œsophagus, and the vertebræ.

The =small splanchnic nerve= (N. splanchnicus minor) is formed by roots derived from the last two or three thoracic ganglia. It runs back with the great splanchnic nerve, but ends in the cœliac or in the renal and adrenal plexuses.

This nerve is not always present and is variable in arrangement. The roots communicate by filaments with the great splanchnic.

4. The =abdominal part= of the sympathetic trunk (Pars abdominalis systematis sympathici) lies along the inner border of the psoas minor, above the aorta on the left side and the posterior vena cava on the right (Fig. 524). The trunk is smaller than the thoracic part, and presents usually six small fusiform =lumbar ganglia= (G. lumbalia), which are connected by rami communicantes with the ventral divisions of the lumbar nerves. Visceral branches go to the aortic and hypogastric plexuses, and to the cœliac and mesenteric ganglia.

5. The =pelvic part= of the sympathetic trunk (Pars pelvina systematis sympathici) begins at the last lumbar ganglion and extends along the pelvic surface of the sacrum internal to the emergence of the ventral branches of the sacral nerves (Fig. 451). At the third segment of the sacrum the trunk divides into internal and external branches. The internal branch inclines to the median plane and unites with the opposite branch. At the junction there is often found the small =coccygeal ganglion= (G. impar), which lies on the coccygeal artery at the joint between the first and second coccygeal vertebræ. A filament from the ganglion accompanies the artery. The external branch communicates with the last two sacral nerves and joins the ventral coccygeal nerves. Ganglia occur near each of the first three sacral foramina, and are connected by gray rami communicantes with the adjacent spinal nerves. The visceral branches are distributed through the hypogastric plexus. They supply motor fibers to the longitudinal and inhibitory fibers to the circular muscular coat of the rectum, motor fibers to the bladder and uterus, and the vasodilator fibers (Nn. erigentes) to the penis.

THE ABDOMINAL AND PELVIC PLEXUSES

The chief plexuses which distribute nerves to the viscera and vessels of the abdominal and pelvic cavities are two in number, the solar and the pelvic. From them fibers proceed to form numerous subsidiary plexuses which are named according to the organs which they supply or the vessels which they enlace.

THE SOLAR PLEXUS

The =solar plexus= (Fig. 450) is situated on the dorsal wall of the abdominal cavity in relation to the aorta and the origin of its chief visceral branches. It comprises the cœliaco-mesenteric ganglia and the cœliac and anterior mesenteric plexuses.

The =cœliaco-mesenteric ganglia=[212] are two in number, right and left. They are situated on each side of the aorta, in relation to the origin of the cœliac and anterior mesenteric arteries. The right ganglion is concealed by the posterior vena cava; it is irregularly quadrilateral and is about two inches (4 to 6 cm.) in length. The left ganglion is largely covered by the left adrenal; it is narrower than the right one and is three or four inches (ca. 8 to 10 cm.) long. The two ganglia are united by irregular connecting branches in front of and behind the anterior mesenteric artery.[213] Each receives the splanchnic nerve of its own side and branches from the dorsal œsophageal continuation of the vagus nerves. Branches from the ganglia and the cords which connect them pass back to the small stellate =posterior mesenteric ganglia=, which are situated at the origin of the posterior mesenteric artery.

The =cœliac plexus= (P. cœliacus) consists of a feltwork of nerve-fibers in which are small ganglia. It surrounds the cœliac artery and from it proceed the following unpaired secondary plexuses which accompany the arterial branches:

1. The =gastric plexus= (P. gastricus) enlaces the gastric artery and divides like the artery into two parts, forming the anterior and posterior gastric plexuses. These receive branches of the vagus nerves.

2. The =hepatic plexus= (P. hepaticus) is formed by several nerves of considerable size which accompany the hepatic artery and the portal vein. It receives fibers from the left vagus, ramifies in the liver, and gives off branches which accompany the collateral branches of the hepatic artery and supply the areas in which these vessels are distributed.

3. The =splenic plexus= (P. lienalis) resembles the preceding in its arrangement. In addition to its terminal branches to the spleen, it gives collateral twigs to the pancreas and the left part of the greater curvature of the stomach.

The =anterior mesenteric plexus= (P. mesentericus cranialis) is formed mainly by branches from the posterior part of the cœliaco-mesenteric ganglia; it is continuous with the cœliac plexus in front and the posterior mesenteric behind. It surrounds the anterior mesenteric trunk and its branches, and supplies the viscera to which these vessels are distributed.

The =posterior mesenteric plexus= (P. mesentericus caudalis) accompanies the artery of like name in its distribution.

The secondary plexuses which accompany the branches of the mesenteric arteries give off branches which form two fine peripheral plexuses in the wall of the intestine. One of these, the =myenteric plexus= (P. myentericus) or plexus of Auerbach, lies between the layers of the muscular coat, and is provided with microscopic ganglia. The other is in the submucous tissue, and is therefore termed the =submucous plexus= (P. submucosus) or plexus of Meissner.

The following paired plexuses are derived mainly from branches of the cœliac and aortic plexuses:

1. The =renal plexuses= (P. renales) proceed largely from the cœliaco-mesenteric ganglia, but receive fibers also from the small splanchnic nerves. They enlace the renal arteries and supply the kidneys. Minute renal ganglia occur on the course of the nerves along the renal vessels.

2. The =adrenal plexuses= (P. suprarenales) are formed by a relatively very large number of fine fibers derived in great part directly from the cœliaco-mesenteric ganglia. Numerous minute ganglia occur in their meshes.

3 a. The =spermatic plexuses= (P. spermatid) proceed largely from the aortic and renal plexuses. Each accompanies the corresponding (internal) spermatic artery to the testicle.

3 b. The =utero-ovarian plexuses= (P. ovarici) are the homologues in the female of the preceding. They accompany the utero-ovarian arteries to the ovary and the cornua of the uterus.

The =hypogastric= or =pelvic plexus= (P. hypogastricus) is the pelvic continuation of the aortic and posterior mesenteric plexuses. The chief nerves which form it enter the pelvic cavity ventral to the large vessels, anastomose with each other and with branches from the third and fourth sacral nerves, and ramify on the pelvic viscera. The peripheral plexuses derived therefrom are named according to the organs which they supply; the chief of these are the =hæmorrhoidal=, =vesical=, =uterovaginal=, =prostatic=, =cavernous= (of the penis or clitoris).

THE NERVOUS SYSTEM OF THE OX[214]

The =spinal cord= resembles that of the horse in conformation and structure. In cattle of medium size its length is about 165 to 170 cm. (ca. 65 to 67 inches) and its weight about 240 to 250 grains (ca. 8 ounces).

In a cow 140 cm. in height Dexler found the weight of the cord (including the intradural nerve-roots) to be 260 g. and the length 162 cm. The lengths of the regions were: cervical 41 cm., thoracic 72 cm., lumbar 32 cm., sacral 7 cm.

The =brain= has an average weight of about 500 grams (ca. 16 to 17 ounces). Its differences in general form are correlated with those noted in the consideration of the cranial cavity.

The =medulla= is short, wide, and thick. Its ventral face is strongly convex. The pyramids are narrow, short, and close together in front. Near the decussation there is a well defined oval prominence on either side which indicates the position of the posterior olive. The corpus trapezoideum is large; it has no central part between the pyramids. The external arcuate fibers are distinct. The restiform bodies are short and thick and diverge more strongly than in the horse. The floor of the fourth ventricle is only about two-thirds as long as in the horse. The area acustica is a well-marked oval prominence lateral to the middle part of the limiting sulcus. The tuberculum acusticum at the origin of the auditory nerve is very large. The anterior fovea is distinct. The posterior recess of the fourth ventricle communicates through the foramen of Magendie (Apertura mediana) with the subarachnoid space.

The =pons= is smaller, both transversely and longitudinally, than that of the horse. It is strongly convex and has a distinct central depression.

The =cerebellum= is smaller and more angular in form than in the horse. The vermis is large and has a distinct depression on its anterior face for the posterior corpora quadrigemina. The hemispheres are relatively small and are not clearly divided into tabulations. The anterior peduncles are very short.

The =cerebral peduncles= are short. A small eminence in the locus perforatus posticus is caused by the presence of the interpeduncular ganglion. The =internal geniculate body= is prominent. The =pineal body= is long and fusiform, and is often pigmented in spots. The third ventricle forms two considerable recesses in relation to the pineal body: one (R. pinealis) extends up into the body; the other (R. suprapinealis) is a long tubular prolongation in front of it.

The =optic tracts= cross the cerebral peduncles almost at a right angle.

The =pituitary body= is situated in a deep fossa and is surrounded by a plexus of vessels.

The =cerebral hemispheres= are shorter, higher, and relatively wider than in the horse. The frontal poles are small, the occipital large. Viewed from the side, the dorsal surface is strongly convex. The highest point of the dorso-medial border is a little in front of its middle and forms a marked prominence termed the =sagittal= or =marginal pole= (Polus sagittalis s. prominentia marginalis dorsalis). Anterior to this the border drops abruptly, being cut into by the deep transverse fissure. The arachnoid on the basal and anterior parts of the hemispheres is usually pigmented. The =corpus callosum= extends through a little more than a third of the length of the hemisphere. The pattern of the =fissures= and =gyri= of the pallium is somewhat simpler than in the horse.

1. The =lateral fissure= (of Sylvius) is very deep. Its middle branch extends almost vertically upward on the middle of the lateral surface of the hemisphere, and is separated by a gyrus of variable width from the suprasylvian fissure. The anterior branch runs forward about parallel with the sulcus rhinalis anterior, from which it is separated by the short gyri of the insula. The latter are covered to a small extent only by the overhanging gyri (operculum). The posterior branch may run back a distance of only about 1.5 cm. and end in T-shaped manner, or it may join the sulcus rhinalis posterior.

2. The =suprasylvian fissure= is deep and very distinct. It extends in an undulating manner from the lateral surface of the occipital pole to the outer side of the sagittal pole. Here it may be interrupted or may be continued by the =coronal fissure=, which descends to the frontal pole and divides into two short branches.

3. The =diagonal fissure= (S. diagonalis) begins in front of the stem of the lateral fissure and runs upward and forward. Its form is very variable.

4. The =transverse fissure= cuts obliquely into the dorsal border in front of the sagittal pole. It is short and deep and commonly communicates with the suprasylvian and coronal fissures.

5. The =marginal fissure= is distinct. It extends from the sagittal pole to the occipital pole. It is flexuous and deviates outward somewhat in its posterior two-thirds.

6. The =entomarginal fissure= lies medial and parallel to the posterior part of the preceding.

7. The =ectomarginal fissure= is lateral and parallel to the marginal fissure. It does not extend so far in either direction as the latter and is often more or less broken up by annectent gyri.

8. The =sulcus rhinalis= is more open than in the horse, since it is not overlapped by the gyri above it.

9. The =calloso-marginal= fissure is flexuous and not so regular as in the horse. It is often interrupted at or near the level of the genu of the corpus callosum, in which case the =genual fissure= continues it downward.

10. The =crucial fissure= is faint and is confined to the medial surface. It lies about one centimeter in front of the transverse fissure and commonly joins the calloso-marginal fissure below.

11. Short and variable fissures occur in front of and behind the middle branch of the lateral fissure (F. ectosylvia anterior, posterior).

The =olfactory bulb= is much smaller than in the horse. The external olfactory tract is large, the inner one small and not distinct.

The =cranial nerves= have in general the same superficial origin as in the horse. The more important differences in other respects are as follows:

The =oculomotor nerve= is larger than in the horse. It emerges with the fourth, sixth, ophthalmic, and maxillary nerves through the large foramen, which is equivalent to the foramen lacerum orbitale and foramen rotundum of the horse.

The internal branch of the =lacrimal nerve= supplies twigs to the mucous membrane of the frontal sinus; the large outer branch runs backward and supplies the matrix of the horn. The =frontal nerve= emerges from the orbit below the supraorbital process. The =naso-ciliary nerve= is large and sends filaments to the ocular muscles. The =ciliary ganglion= is somewhat larger than in the horse and is connected with the lower division of the oculomotor nerve by several short filaments. In consequence of the absence of the canine and upper incisor teeth the corresponding branch of the infraorbital nerve is naturally wanting. The =mandibular nerve= emerges through the foramen ovale. The =superficial temporal nerve= gives off a large branch which joins the superior buccal division of the facial on the masseter, about half-way between the zygomatic arch and the angle of the jaw. The =otic ganglion= is larger than in the horse. According to Moussu the buccinator nerve furnishes excito-secretory twigs to the parotid and inferior buccal glands.

The =facial nerve= divides into its two terminal branches before reaching the border of the jaw. The =superior buccal nerve= is the larger of the two; it crosses the masseter much lower than in the horse. The relatively small =inferior buccal nerve= runs beneath the parotid or in the gland substance parallel with the border of the lower jaw, crosses under the insertion of the sterno-cephalicus, and runs forward along the depressor labii inferioris. At the point where it crosses the facial vein and parotid duct it gives off an anastomotic branch to the superior nerve. The =auriculo-palpebral nerve= is large.

The =vagus= bears—in addition to the relatively large =jugular ganglion=—a =ganglion nodosum= at the point of origin of the superior laryngeal nerve. The trunk is large. The =pharyngeal branch= is large and anastomoses with the superior and external laryngeal nerves. The latter commonly arises directly from the trunk. The =superior œsophageal trunk= communicates with the splanchnic nerve, contributes twigs to the hepatic plexus, and ramifies chiefly on the right surface of the rumen and the adjacent surface of the abomasum. The =inferior œsophageal trunk= supplies branches to the hepatic plexus and to all the divisions of the stomach.

The =spinal accessory nerve= presents two special features. The part which joins the jugular ganglion bears a small ganglion. The ventral branch supplies both parts of the sterno-cephalicus.

The =hypoglossal nerve= is large. It is connected with the ventral division of the first cervical nerve by a branch of considerable size, and detaches a long branch which runs backward along the carotid artery.

The =spinal nerves= resemble those of the horse in origin and general arrangement. The thoracic nerves number thirteen pairs. The more important differences in the limb-plexuses and their branches are as follows:

The =brachial plexus= is formed by the ventral branches of the last three cervical and first thoracic nerves; the second thoracic nerve furnishes no root, but the ventral branch of the sixth cervical goes almost entirely to the plexus after giving off the nerve to the rhomboideus and the cervical part of the serratus magnus.

The differences in the nerves above the elbow are not of sufficient moment to receive notice in this brief account, but below this point there are naturally important special features correlated chiefly with the arrangement of the digits.

The =radial nerve= is continued below the elbow by a large =cutaneous branch= (N. cutaneus antibrachii dorsalis) which emerges at the lower border of the external head of the triceps and descends on the dorsal aspect of the limb. It communicates above the carpus with the cutaneous branch of the median nerve and terminates in three =dorsal digital nerves=; two of these descend along the axial or interdigital side of the dorsal surface of the chief digits, and the third along the inner (abaxial) side of the inner chief digit.

The =ulnar nerve= divides at a variable distance down the forearm into two branches. The =dorsal= or =superficial branch= emerges between the tendons of the external and middle flexors of the carpus, and is continued as the =external dorsal digital nerve= on the outer chief digit. The =volar= or =deep branch= descends along the superficial digital flexor, gives a branch to the suspensory ligament below the carpus, and unites with the external branch of the median nerve to form the =external volar digital nerve=.

The =median nerve= is much larger than the ulnar. It passes beneath the pronator teres, descends the forearm as in the horse, and divides in the distal part of the metacarpus into two branches. The =internal branch= gives twigs to the inner small digit and is continued on the inner side of the volar surface of the inner chief digit as the =internal volar digital nerve= (N. digitalis medialis digiti III); it also concurs with the outer branch in forming the two digital nerves which descend along the interdigital aspect of the chief digits. The =external branch= is larger. It bifurcates, and one division unites with the twig from the internal branch to form a common digital trunk. From the latter two digital nerves proceed as mentioned above; these are the =external= and =internal volar digital nerves= of the internal and external chief digits respectively (N. digitalis volaris lateralis digiti III, medialis digiti IV). The other division unites with the volar branch of the ulnar nerve to form the =external volar digital nerve= of the external chief digit (N. digitalis lateralis digiti IV).

The =lumbo-sacral plexus= and its branches to the pelvis and thigh present no very striking special features.

The =superficial peroneal nerve= is much larger than in the horse. After crossing beneath the peroneus longus it passes down on the front of the tarsus and metatarsus and divides into three branches. The internal and external branches descend as the =internal= and =external dorsal digital nerves= on the chief digits. The larger middle branch joins a branch of the deep peroneal nerve in the interdigital space, and from this union proceed the =dorsal digital nerves= which descend on the opposed surfaces of the chief digits.

The =deep peroneal nerve= descends in the leg as in the horse and continues down the anterior groove of the metatarsus with the dorsal metatarsal artery. Its terminal branches concur with branches from the superficial peroneal nerve in the formation of the two axial =dorsal digital nerves= (N. dig. dors. lat. dig. III et dig. dors. med. dig. IV pedis), and with a branch of the internal plantar nerve in the formation of corresponding plantar digital nerves.

The =tibial nerve= divides at the back of the hock into internal and external plantar nerves. The =internal plantar nerve= descends between the superficial flexor tendon and the suspensory ligament and divides into two branches; the inner branch descends as the =internal plantar digital nerve= (N. dig. plant. med. dig. III) along the inner side of the flexor tendons of the inner chief digit; the outer branch turns around the flexor tendons to reach the interdigital space, where it concurs with a branch of the deep peroneal nerve in the formation of two =axial plantar digital nerves= (N. dig. plant. lat. dig. III et dig. plant. med. dig. IV) which descend on the opposed surfaces of the chief digits. The =external plantar nerve= descends along the outer border of the flexor tendons, gives a branch to the suspensory ligament and to the external small digit, and continues along the outer face of the external digit as the =external plantar digital nerve= (N. dig. plant. lat. dig. IV).

The =sympathetic system= closely resembles that of the horse in its general arrangement, and only a few differential features will receive attention. The =superior cervical ganglion= is closer to the cranial base and is thicker than in the horse; its branches to the carotid and cavernous plexuses are large, and no connection is formed with the spinal accessory nerve. The =cervical trunk= is smaller than in the horse, and arises by two or three bundles from the superior cervical ganglion behind its middle. The =inferior cervical ganglion= is distinctly separable from the first thoracic; the latter is large. There are thirteen pairs of =thoracic ganglia=. The =cœliaco-mesenteric ganglia= are plexiform, not compact. There are five pairs of =sacral ganglia=, and the right and left trunks are connected here by transverse anastomoses.

THE NERVOUS SYSTEM OF THE PIG

The =spinal cord= weighs about 42 grams (Ellenberger-Baum). It is almost circular in cross-section, except at the enlargements, where it is somewhat flattened dorso-ventrally. The conus medullaris extends to the anterior part of the third sacral segment. The epidural space is occupied by a large quantity of fat.

The =brain= in adults of medium size weighs about 125 grams (ca. 4 to 4½ ounces). When viewed from above, it is seen to have an elongated oval form. The occipital poles overlie the cerebellum to a small extent only; the frontal poles are rounded and relatively large, but do not conceal the ends of the olfactory bulbs. The =medulla= is relatively broad. The cuneate tubercle is very large and is limited externally by a groove. The corpus trapezoideum is very wide laterally. The =pons= is less prominent than in the ox. The =cerebellum= is very wide and short. Its anterior face is flattened and presents a depression for the corpora quadrigemina. The vermis is large. The hemispheres consist of an inner large and an outer small part. The =cerebral peduncles= are very short. The posterior corpora quadrigemina are wide apart, rounded, and relatively large. The internal geniculate body is prominent. The =cerebral hemispheres= are somewhat bean-shaped in lateral profile, the convex border being dorsal. The arrangement of the gyri and sulci is simpler than in the horse or ox. The principal fissures are as follows:

1. The =lateral fissure= (of Sylvius) begins at the sulcus rhinalis and runs upward and somewhat backward on the depressed part of the lateral surface of the hemisphere; it appears unbranched on superficial examination, but when the gyrus which almost completely conceals the insula is raised, an anterior branch is exposed which forms the dorsal boundary of the insula.

2. The =suprasylvian fissure= pursues a curved course approximately parallel with the dorso-medial border of the hemisphere. Its posterior end is separated by a short interval from the sulcus rhinalis posterior. From its highest point a branch proceeds obliquely upward and forward, crosses the dorso-medial border, and joins the splenial fissure.

3. The =diagonal fissure= crosses the anterior part of the lateral surface. It is directed obliquely downward and backward.

4. The =coronal fissure= is constant and deep. It is directed upward and inward over the frontal pole, continues backward near the dorso-medial border, and usually ends by passing obliquely over the border to the inner surface of the hemisphere.

5. The =presylvian fissure= begins—apparently as a branch of the sulcus rhinalis anterior—about 2 cm. in front of the lateral fissure, and curves over the lateral aspect of the frontal pole.

6. The =marginal fissure= begins behind the cruciate fissure close to the dorso-medial border and extends in a gentle curve backward almost to the occipital pole.

7. The =ectomarginal fissure= lies above and nearly parallel to the posterior part of the suprasylvian fissure.

8. The =entomarginal fissure= lies along the posterior part of the dorso-medial border.

9. The =calloso-marginal fissure= consists of two separate parts. The more extensive posterior part is termed the =splenial fissure=. It extends from the tentorial aspect of the hemisphere in a direction parallel with the corpus callosum nearly to the middle of the medial surface; it is continued by the cruciate fissure and is also connected with the suprasylvian and coronal fissures by branches which pass obliquely upward and forward. The anterior part, the =genual fissure=, lies about midway between the anterior part of the corpus callosum and the dorso-medial border.

10. The =cruciate fissure= is short and shallow. It runs obliquely upward and forward from the anterior end of the splenial fissure on the inner surface of the hemisphere.

11. The =sulcus rhinalis= extends in an undulating manner along the entire lower part of the lateral surface of the hemisphere and forms the upper limit of the rhinencephalon.

The =olfactory bulbs= are very large and the =tracts= extremely broad and short. The trigonum olfactorium is so prominent as to be termed the =tuberculum olfactorium=.

The =cranial nerves= present the following special features:

The =third=, =fourth=, =sixth=, and the =ophthalmic= and =maxillary divisions= of the fifth nerve, emerge together as in the ox.

The =lacrimal nerve= resembles that of the horse, the =frontal= that of the ox. The =naso-ciliary nerve= is relatively large and sends numerous filaments to the ocular muscles. The =maxillary nerve= has a very short course in the pterygo-palatine fossa. The =infraorbital nerve= is large in correlation with the development of the snout which receives numerous branches. The =mandibular nerve= emerges through the foramen lacerum anterius. The =superficial temporal nerve= is small; according to Moussu it furnishes the excito-secretory fibers to the upper part of the parotid gland, while those going to the lower part are derived from the mylo-hyoid nerve.

The =inferior buccal nerve= passes downward and forward under cover of the parotid gland and accompanies the parotid duct, with which it turns around the lower border of the jaw in front of the masseter.

The =vagus= bears a =jugular ganglion= and a =ganglion nodosum=; the latter occurs at the point of origin of the superior laryngeal nerve, and may be as large as a small pea. Proximal to this the vagus is easily divided into two strands, one of which is the accessory component. The œsophageal trunks form a posterior œsophageal plexus, as in man, from which two nerves issue. The inferior nerve is small and ramifies on the parietal surface of the stomach. The superior trunk is much larger; it gives branches to the stomach, crosses the lesser curvature of that organ, and joins the solar plexus.

The =hypoglossal nerve= may present a small dorsal root, on which there is a minute hypoglossal ganglion (of Froriep).

The =spinal nerves= number on each side eight in the cervical region, fourteen (commonly) in the thoracic, seven in the lumbar, and four in the sacral. Some of the special features of the nerves of the limbs are as follows:

The =brachial plexus= is derived from the same nerves as in the ox, but the root furnished by the sixth cervical is relatively smaller. The plexus consists of two parts, the upper of which emerges above the scalenus, the lower between the two parts of that muscle. The more important differences in the nerves emanating from the plexus from the arrangement in the ox occur in the lower part of the limb. The cutaneous branch of the =radial nerve= divides at the carpus into branches which concur with the dorsal branch of the ulnar nerve in supplying the =dorsal digital nerves=, two for each digit. The =volar digital nerves=, also two for each digit, are formed by the terminal branches of the =median nerve= and the volar or deep branch of the =ulnar nerve=. The formation and arrangement of the digital nerves are indicated in the annexed schematic figures.

The =lumbo-sacral plexus= is derived from the ventral branches of the last three lumbar and first sacral nerves. The distribution of the branches of the plexus differs chiefly in the distal part of the limb. The =superficial peroneal nerve= is large and terminates by forming the greater part of the =dorsal digital nerves=. The latter, two for each digit, are also in part formed by the terminal branches of the =deep peroneal nerve=.

The =tibial nerve= divides at the tarsus into =internal= and =external plantar nerves=. The latter divide to form the =plantar digital nerves=, two for each digit. In addition, the external plantar nerve supplies a branch to the dorsal aspect of the outer (fifth) digit. The arrangement of the digital nerves is indicated by the annexed schematic figures.

The =sympathetic system= of the pig has received very little attention from anatomists. The =superior cervical ganglion= is long and fusiform. It gives off filaments which join the vagus near the ganglion nodosum. The =cervical trunk= is short and relatively larger than in the ox; it is inclosed in a common sheath with the vagus in the neck and separates from that nerve to join the =middle cervical ganglion= at the thoracic inlet.

THE NERVOUS SYSTEM OF THE DOG

The =spinal cord= is almost circular in cross-section except at the well-marked cervical and lumbar enlargements, where it is compressed dorso-ventrally. The conus medullaris lies over the junction of the sixth and seventh lumbar vertebræ. The length of the cord of a rather large dog was found to be about 38 cm.; of this, the cervical part was 11 cm., the thoracic 17.4 cm., the lumbar about 7 cm., and the sacro-coccygeal about 2.6 cm. (Flatau-Jacobson).

The =brain= weighs about 60 to 70 g. in dogs of medium size, but there is, of course, a wide range of weight in the different breeds. Thus in small terriers the weight is 30 g. or even less, while in very large dogs it may exceed 150 g. It corresponds much more closely with the cranium in size and general form than in the animals previously described; this is specially true of the small breeds, in which the bony crests and frontal sinuses are little developed.

The =medulla= is broad and thick. Its ventral surface is strongly convex from side to side. The pyramids are large and prominent and are limited by distinct median and lateral grooves. The olivary eminence is a well defined oval elevation situated between the pyramid and the superficial origin of the hypoglossal nerve. The external arcuate fibers form a wide band which crosses the lateral surface obliquely upward and forward, and obscures the groove which limits the restiform body externally. The cuneate tubercle is distinct. The rhomboid fossa is deep and narrow.

The =pons= is relatively small. The =corpus trapezoideum= is very wide and is divided by the pyramids into two lateral parts. The =cerebellum= is very broad, but is low and also compressed from before backward. Rather more than half of it is overlapped by the cerebral hemispheres. The anterior surface is accurately adapted to the concave tentorial surfaces of the hemispheres and to the posterior corpora quadrigemina and their commissure. The posterior surface is almost vertical and is convex centrally and flattened laterally. The vermis is prominent and in general well defined, although it is connected in its middle part with the hemispheres. The latter are three-sided and consist of four lobules. The anterior peduncles are very short.

The =posterior corpora quadrigemina= are large, very wide apart, and prominent, and are connected by a curved commissure. The =internal geniculate body= is large. In the deep interpeduncular fossa are two small bands which indicate the course of the fasciculi retroflexi, tracts which connect the habenular and interpeduncular ganglia. The =mammillary body= is double. The =tuber cinereum= is relatively large. The =pituitary body= is circular and rather small.

The =cerebral hemispheres= are very broad behind and diminish in width anteriorly; there is a sudden narrowing at the frontal poles, which are flattened laterally. The tentorial surfaces are concave and form a deep cavity which receives the anterior part of the cerebellum. The arrangement of the fissures and gyri is simpler than in the animals previously examined. The chief fissures are as follows:

1. The =lateral fissure= (of Sylvius) extends upward and backward from the sulcus rhinalis a little behind the middle of the lateral surface of the hemisphere.

2. The =ectosylvian fissure= has approximately the shape of an inverted u, and curves over the lateral fissure. It is regarded as consisting of three parts—anterior, middle, and posterior (F. ectosylvia anterior, media, posterior).

3. The =suprasylvian fissure= lies above and approximately concentric with the preceding. It also consists of three parts—anterior, middle, and posterior.

4. The =ectomarginal= or =collateral fissure= runs forward on the dorsal aspect of the hemisphere almost parallel with the dorso-medial border. A little in front of the middle of the surface it gives off a short =ansate fissure= (F. ansata) which runs obliquely inward and forward, and is continued by the coronal fissure.

5. The =coronal fissure= is the continuation of the ectomarginal. It runs forward and downward, curving around the cruciate fissure, and ends behind the middle of the presylvian fissure.

6. The =ectolateral fissure= lies between the posterior part of the ectomarginal fissure and the suprasylvian fissure.

7. The =entomarginal fissure= lies between the anterior part of the ectomarginal fissure and the dorso-medial border. It is often indistinct and not rarely absent.

8. The =presylvian fissure= begins at the sulcus rhinalis, a little in front of its middle, and curves over the anterior third of the lateral surface of the hemisphere in front of the coronal fissure.

9. The =cruciate fissure= is the deepest and most characteristic. It cuts deeply into the anterior third of the dorso-medial border and runs almost straight outward. It is continuous on the inner surface of the hemisphere with the calloso-marginal or splenial fissure.

10. The =sulcus rhinalis= is continued on the tentorial surface of the hemisphere by the occipito-temporal fissure. Anteriorly it is prolonged as the olfactory fissure, which is concealed by the olfactory bulb and tract.

11. The =calloso-marginal= or =splenial fissure= is parallel with the splenium and middle part of the corpus callosum on the inner surface of the hemisphere. It is continuous in front with the cruciate fissure and runs downward and outward across the tentorial surface to join the occipito-temporal fissure and sulcus rhinalis. It gives off from its highest part the short lesser or accessory cruciate fissure.

12. The =suprasplenial fissure= runs almost parallel with the posterior part of the calloso-marginal fissure on the inner and tentorial surfaces of the hemisphere.

The =olfactory bulb= is large and is strongly compressed laterally; its anterior end projects beyond the frontal pole of the hemisphere. The tract is short and is also flattened laterally. Both contain a narrow cavity which communicates with the lateral ventricle. The =pyriform lobe= is large and rounded.

The =cranial nerves= present the following special features which are worthy of notice:

The =ophthalmic nerve= gives off lacrimal, frontal, long ciliary, ethmoidal, and infratrochlear branches. The =lacrimal nerve= arises from the ophthalmic at its origin;[215] its recurrent branch emerges at the orbital ligament and concurs with the zygomatic and frontal nerves in the formation of the anterior auricular plexus. The =frontal nerve= emerges from the orbit in front of the upper end of the orbital ligament, ramifies in the upper lid and the adjacent skin of the forehead, and sends branches backward to the anterior auricular plexus. The =long ciliary nerve= accompanies the optic nerve and divides into several branches which pierce the posterior part of the sclera. The =ethmoidal nerve= gives off internal nasal branches and ends in the muzzle. The =infratrochlear nerve= runs forward between the internal straight and the superior oblique muscles of the eye and ramifies on the face in the vicinity of the inner canthus.

The =maxillary nerve=, after giving off the zygomatic, divides into infraorbital and sphenopalatine branches. The =zygomatic nerve= emerges through an opening in the upper part of the orbital ligament and ramifies in the lower lid and on the adjacent surface of the face. The =infraorbital nerves=, two in number, divide within the infraorbital canal and after their emergence upon the face, thus forming seven or eight =external nasal= and =superior labial branches=. The =sphenopalatine nerve= gives off =lesser= and =greater palatine= and =posterior nasal nerves=.

The =mandibular nerve= passes out through the foramen ovale. The =superficial temporal nerve= divides into auricular, temporal, and malar branches; the last-named crosses the masseter and ramifies with the buccal nerves. The =mylo-hyoid nerve= is given off from the mandibular nerve almost immediately after the latter emerges from the cranium; it innervates the mylo-hyoideus and digastricus and gives off a branch which turns around the lower jaw, joins the inferior buccal nerve, and ramifies on the lateral surface of the face. The =inferior alveolar nerve= arises by a common trunk with the mylo-hyoid; it gives off dental branches and terminates in mental and inferior labial branches. The =lingual nerve= supplies vasodilator and excito-secretory filaments to the submaxillary and sublingual salivary glands; these fibers are derived from the chorda tympani.

The =facial nerve= divides near the posterior border of the jaw into four branches. The upper branch is the =auriculo-palpebral nerve=, which divides after a very short course into anterior auricular and zygomatic branches. The latter curves upward and forward across the zygomatic arch toward the eye, and divides into branches which supply the eyelids and nasal region and concur with the frontal and lacrimal nerves in forming the anterior auricular plexus. The =superior buccal nerve= accompanies the parotid duct across the masseter. The =inferior buccal nerve= runs forward along the lower border of the masseter and the mandible. The two nerves ramify on the cheek and anastomose with each other and the infraorbital nerves to form a plexus from which branches go to the muscles of the lips and nostrils. The =cervical branch= runs downward and backward over the submaxillary gland and ramifies in the cervical panniculus; it communicates with the inferior buccal nerve and sends twigs to the parotido-auricularis muscle and the submaxillary space.

The =vagus= bears a =jugular ganglion= and a =ganglion nodosum=. The latter is situated near the superior cervical ganglion on the rectus capitis anterior major and dorsal to the carotid artery; it is fusiform and may be about half an inch (ca. 1 to 1.5 cm.) long in a large dog. In its course in the neck the nerve is inclosed with the sympathetic trunk in a common sheath and is related ventrally to the common carotid artery. The formation of dorsal and ventral =œsophageal trunks= by the union of the dorsal and ventral divisions of the two nerves takes place at the hiatus œsophageus. The =dorsal trunk= concurs with branches of the solar plexus in forming the =posterior gastric plexus= on the visceral surface of the stomach. The =ventral trunk= ramifies on the parietal surface of the stomach, forming the =anterior gastric plexus=, from which a considerable branch passes along the lesser curvature to the pylorus. Some special features of the collateral branches are: Two pharyngeal branches are present. The =superior pharyngeal branch= arises from the vagus above the ganglion nodosum. It passes under the deep face of the carotid artery and descends on the lateral surface of the pharynx to end in the crico-thyroid muscle. It furnishes a root of the inferior pharyngeal branch, and communicates with the pharyngeal branch of the ninth and with the superior laryngeal and hypoglossal nerves. The =inferior pharyngeal branch= is formed by the union of roots derived from the superior pharyngeal nerve and the ganglion nodosum, together with filaments from the superior cervical ganglion. It crosses the side of the pharynx behind the superior pharyngeal and ramifies on the posterior constrictor of the pharynx and the origin of the œsophagus. It contributes filaments to the pharyngeal plexus, communicates with the recurrent nerve, and supplies twigs to the thyroid gland. The =pharyngeal plexus= is formed on the lateral surface of the pharynx by branches of the pharyngeal nerves and the communications above described; branches from it innervate the muscles and mucous membrane of the pharynx. The =superior laryngeal nerve= arises from the ganglion nodosum and descends over the side of the pharynx, crossing beneath the carotid artery and the superior laryngeal nerve. It passes through the thyroid notch and ramifies in the mucous membrane of the larynx. It communicates with the superior cervical ganglion and the superior pharyngeal branch of the vagus, and gives twigs to the hyo-pharyngeus muscle. Immediately after its entrance into the larynx it gives off a large branch which, instead of uniting with the recurrent as in the other animals, has a peculiar arrangement. It runs back near the dorsal border of the thyroid cartilage, gives a branch to the crico-arytenoideus posterior as it passes over that muscle, and continues along the trachea internal to the recurrent nerve. At the thoracic inlet it communicates with the inferior cervical ganglion and continues backward to unite with the vagus at or near the point of origin of the recurrent nerve. Its collateral filaments supply the trachea and concur with the inferior pharyngeal branch in forming a plexus on the cervical part of the œsophagus which innervates that tube.[216] The =depressor nerve= is a very delicate filament which arises usually from the superior laryngeal nerve and accompanies the vago-sympathetic trunk to the thorax; its fibers reach the heart through the cardiac nerves. The =pulmonary= and =posterior œsophageal plexuses= are highly developed.

The =hypoglossal nerve= gives off a long branch (R. descendens) which runs downward and backward across the pharynx and larynx, communicates with the ventral branch of the first cervical nerve, and supplies the thyro-hyoid, sterno-hyoid, and sterno-thyroid muscles.

The =spinal nerves= number thirty-six or thirty-seven on either side, and comprise eight cervical, thirteen thoracic, seven lumbar, and five or six coccygeal.

The =brachial plexus= (Fig. 487) is derived from the ventral branches of the last four cervical and first thoracic nerves; the root supplied by the fifth cervical nerve is very small. The roots unite at the lower border of the scalenus. The more important special features in the arrangement of the nerves which emanate from the plexus are as follows:

The =musculo-cutaneous nerve= passes between the coraco-brachialis and the brachial artery and descends in the arm in front of the artery. At the shoulder joint it gives off branches to the biceps and coraco-brachialis, and in the lower third of the arm is connected with the median nerve by an oblique branch. It terminates near the elbow by dividing into a branch for the brachialis and a small cutaneous nerve which passes down over the inner face of the elbow and, inclining a little forward, descends over the deep fascia of the forearm to the carpus.

The =radial nerve= descends behind the ulnar nerve, gives branches to the extensors of the elbow, dips in between the internal head of the triceps and the accessory head of the anconeus, winds around the arm, and divides between the brachialis and the external head of the triceps into two branches. The =deep branch= (R. profundus) supplies the extensor and supinator muscles on the forearm. The =superficial branch= (R. superficialis) emerges upon the flexor surface of the elbow and divides into two branches which terminate by supplying two =dorsal digital nerves= to each digit, except the fifth, which receives its outer dorsal nerve from the ulnar. The inner branch descends along the inner side of the cephalic vein to the carpus, where it divides into dorsal digital nerves for the first digit and the inner side of the second. The outer branch is much larger. It runs downward on the middle of the front of the forearm and supplies the remaining dorsal digital nerves except that to the outer side of the fifth digit.

The =ulnar nerve= is as large as or larger than the median, with which it is united for some distance. At the distal third of the arm it separates from the median and passes over the internal epicondyle of the humerus. At the proximal part of the forearm it gives off the =dorsal branch= (R. dorsalis), which supplies cutaneous twigs to the dorso-lateral surface of the lower part of the forearm and carpus and terminates as the =external dorsal digital nerve= of the fifth digit. Descending under cover of the flexor carpi ulnaris, the ulnar nerve inclines inward under the tendon of insertion of that muscle and divides into superficial and deep branches. The =superficial branch= (R. superficialis) runs downward along the outer border of the flexor tendons, gives off the =external volar digital nerve of the fifth digit= (N. dig. vol. lat. dig. V), and a branch (N. met. vol. IV) which descends in the space between the fourth and fifth metacarpal bones and unites with the deep branch. The =deep branch= (R. profundus) descends in the carpal canal and divides under the deep flexor tendon into its terminal branches. The smaller of these supply the volar metacarpal muscles. The larger terminals are the three =volar common digital nerves= (Nn. dig. vol. comm. II, III, IV), which descend along the second, third, and fourth intermetacarpal spaces, subdivide, and concur with the volar metacarpal branches of the median nerve in forming the =volar proper digital nerves= (Nn. dig. vol. proprii).

The =median nerve= descends behind the brachial artery, passes over the internal epicondyle of the humerus, then under the pronator teres, and continues in the forearm under cover of the flexor carpi radialis. It gives branches below the elbow to the flexor and pronator muscles, and lower down a palmar branch to the skin on the inner and posterior aspect of the carpus, and terminates between the superficial and deep flexor tendons by dividing into three =volar metacarpal nerves= (N. met. vol. I, II, III). These descend in the first, second, and third intermetacarpal spaces and unite with the volar common digital nerves in forming volar proper digital nerves. The arrangement of the digital nerves is indicated in the annexed schematic figures.

The =lumbo-sacral plexus= is formed from the ventral branches of the last five lumbar and first sacral nerves. The more important special facts in regard to the nerves of the pelvic limb are as follows:

The =saphenous nerve= (Fig. 492) is relatively large, and, in fact, might be considered as the continuation of the femoral nerve. It descends at first in front of the femoral artery, then passes over the lower part of the inner surface of the thigh with the saphenous artery, continues down the leg with the dorsal branch of that vessel, and anastomoses with branches of the superficial peroneal nerve. It supplies cutaneous twigs from the stifle to the metatarsus.

The =peroneal nerve= separates from the tibial above the origin of the gastrocnemius, runs downward and forward across the outer head of that muscle, passes between the deep flexor of the digit and the peroneus longus, and divides into superficial and deep branches. The =superficial peroneal nerve= descends the leg along the peroneus tertius and longus, gives off a =dorsal branch= to the first digit (N. cutaneus dorsalis medialis), and divides at the proximal part of the metatarsus into three =dorsal common digital nerves= (Nn. dig. pedis dors. comm. II, III, IV). These descend with the superficial dorsal metatarsal arteries and concur with branches of the deep peroneal nerve in forming =dorsal proper digital nerves= (Nn. dig. ped. prop. dorsales). The =deep peroneal nerve= passes down the leg with the anterior tibial vessels. It gives twigs to the hock joint and the extensor brevis muscle, and divides into three =dorsal metatarsal nerves= (Nn. met. dors. II, III, IV); these descend with the corresponding arteries along the intermetatarsal spaces and unite with the dorsal common digital nerves in supplying the dorsal proper digital nerves.

The =tibial nerve= divides at the tarsus into two plantar branches. The =internal plantar nerve= descends along the inner border of the superficial flexor tendon and divides near the middle of the metatarsus into two branches. Of these, the internal branch constitutes the =first plantar common digital nerve= (N. dig. comm. plant. I). The outer branch descends on the superficial flexor tendon and divides into three =plantar metatarsal nerves= (Nn. met. plant. II, III, IV), which unite with the plantar common digital nerves. The =external plantar nerve= passes down between the flexor tendons, sends twigs to the muscles on the plantar surface of the metatarsus, and divides into three =plantar common digital nerves= (Nn. dig. comm, plant. II, III, IV). These descend with the deep plantar metatarsal arteries in the second, third, and fourth intermetatarsal spaces, receive the plantar metatarsal nerves, and divide into =plantar proper digital nerves=, which pass down the opposed surfaces of the second to the fifth digits.

The =sympathetic system= presents few special features worthy of mention. The =superior cervical ganglion= lies above the ganglion nodosum close to the cranial base and internal to the origin of the internal carotid and occipital arteries. It forms connections directly or through the carotid plexus with the last seven cranial and first cervical nerves. The =cervical trunk= unites with the vagus so intimately as to form a vago-sympathetic trunk. There may be a small =middle cervical ganglion= in front of the inferior cervical ganglion. The latter is usually distinct from the first thoracic ganglion, which is stellate and lies on the longus colli opposite the second rib and intercostal space.

ÆSTHESIOLOGY

THE SENSE ORGANS AND COMMON INTEGUMENT

The =organs of the senses= (Organa sensuum) receive external stimuli and conduct impulses to the brain which result in sensations of sight, hearing, taste, smell, and touch. They consist essentially of specially differentiated cells, the neuro-epithelium, and a conduction path which is simple in the more generalized sense organs, elaborate in those which are highly specialized—the eye and the ear.

THE SENSE ORGANS AND SKIN OF THE HORSE

THE EYE

The =eye= or =organ of vision= (Organon visus) in the broader sense of the term comprises the eyeball or globe of the eye, the optic nerve, and certain accessory organs associated therewith. The accessory organs (Organa oculi accessoria) are the orbital fasciæ and muscles, the eyelids and conjunctiva, and the lacrimal apparatus. These structures will be considered in the order in which they may be most conveniently examined, taking the horse as a type. The bony walls of the orbit have been described in connection with the skull; the periorbita, a fibrous membrane which incloses the eyeball together with its muscles, vessels, and nerves, may be appropriately included in the account of the fasciæ.

THE EYELIDS AND CONJUNCTIVA

The =eyelids=, upper and lower (Palpebra superior et inferior), are movable folds of integument situated in front of the eyeball. When closed, they cover the entrance to the orbit and the anterior surface of the eyeball. The upper lid is much more extensive and more movable than the lower one, and its free edge is more concave. The interval between the lids is termed the =palpebral fissure= (Rima palpebrarum). When the eye is closed, it is an oblique slit about two inches (ca. 5 cm.) in length; when open, it is biconvex in outline. The ends of the fissure are the =angles= or =canthi=, and are distinguished as =internal= or =nasal=, and =external= or =temporal= (Angulus oculi medialis, lateralis). The external angle is rounded when the eye is open, but the internal angle is narrowed to form a ᑐ-shaped bay or recess, termed the =lacrimal lake= (Lacus lacrimalis). In this there is a rounded, pigmented prominence known as the =lacrimal caruncle= (Caruncula lacrimalis); it is about the size of a small pea and is covered with modified skin, connected with that of the inner commissure, from which project a number of hairs provided with sebaceous glands. The lids unite on either side and form the =commissures=, internal and external (Commissura palpebrarum medialis, lateralis). The =anterior surface= of the lids (Facies anterior palpebrarum) is convex and presents a variable number of long tactile hairs in addition to the ordinary but very short hairs. A considerable number of tactile hairs are scattered over the lower part of the lower lid, but on the upper lid they are very scanty. The infrapalpebral depression (Sulcus infrapalpebralis) indicates somewhat indistinctly the limit of the lower lid. The upper lid is marked by two furrows when raised. The =posterior surface= (Facies posterior palpebrarum) is adapted to the free surface of the eyeball and is covered by the palpebral conjunctiva. The free border of the lid is smooth and usually black. It has a well defined posterior margin (Limbus palpebralis posterior), along which the ducts of the tarsal glands open. The anterior margin (Limbus palpebralis anterior) bears stiff hairs termed the cilia or eyelashes. On the upper lid the cilia are long and numerous except at its inner third, where they are very small or absent. On the lower lid the cilia are often scarcely distinguishable from the ordinary hairs; in other cases they may be clearly seen except near the external canthus, and are much finer and shorter than those of the upper lid. The edge of each lid is pierced near the internal angle by a minute, slit-like opening, the =punctum lacrimalis=, which is the entrance to the lacrimal duct or canaliculus.

=Structure of the Eyelids.=—The skin of the eyelids is thin and freely movable, except near the free edge, where it is more firmly attached. The underlying subcutaneous tissue is destitute of fat. The =muscular layer= consists chiefly of the elliptical bundles of the orbicularis oculi, with which are associated fibers of the corrugator supercilii in the upper lid and the malaris in the lower lid. At the inner side there is a fibrous band, the =palpebral ligament=, which is attached to the lacrimal tubercle and furnishes origin to some fibers of the orbicularis. At the inner commissure a bundle detached from the orbicularis passes inward behind the lacrimal sac, and is known as the pars lacrimalis or Horner’s muscle. At the outer side an indistinct palpebral raphé occurs where fibers of the orbicularis decussate. The =fibrous layer= is thicker and denser along the free edge of the lid, forming here the =tarsus=. The tarsus furnishes insertion to a layer of unstriped muscle known as the tarsal muscle (of Müller). The =tarsal glands= (Glandulæ tarsales) are partly embedded in the deep face of the tarsus, and are visible when the lid is everted if the conjunctiva is not too strongly pigmented. They are arranged in a linear series, close together, and with their long axes perpendicular to the free edge of each lid. In the upper lid they number forty-five to fifty; in the lower, thirty to thirty-five. Each consists of a tubular duct beset with numerous alveoli, in which a fatty substance, the =palpebral sebum=, is secreted. The =palpebral conjunctiva= lines the posterior surface of the eyelids.

The =conjunctiva= is the mucous membrane which lines the lids as =palpebral conjunctiva= (C. palpebrarum) and is reflected upon the anterior part of the eyeball as =bulbar conjunctiva= (C. bulbi); the line of reflection is termed the =fornix conjunctivæ=. The palpebral part is closely adherent to the tarsus, but is loosely attached further back. It is papillated and is covered with stratified cylindrical epithelium in which many goblet cells are present. In the fornix and its vicinity there are tubular glands (of Henle). Near the inner angle there are numerous lymph nodules. The conjunctiva of the outer part of the upper lid is pierced near the fornix by the orifices of the excretory ducts of the lacrimal gland. The bulbar conjunctiva is loosely attached to the anterior part of the sclera and is pigmented in the vicinity of the corneo-scleral junction. On the cornea it is represented by a stratified epithelium.

When the lids are in apposition, the conjunctiva (including the epithelium of the cornea) forms a complete =conjunctival sac=, as the capillary space between the lids and the eyeball is termed.

The =third eyelid= (Palpebra tertia) is situated at the inner angle of the eye (Figs. 551, 556). It consists of a semilunar fold of the conjunctiva, known as the =membrana nictitans=, which covers and partly incloses a curved plate of hyaline cartilage. Its marginal part is thin and usually more or less pigmented. The cartilage has an elongated quadrilateral outline. The part of it which lies in the membrana is wide and thin. The deep part is narrower and thicker and is embedded in fat at the inner side of the eyeball. Numerous minute lymph nodules occur in the membrana nictitans, and the deep part of the cartilage is surrounded by a gland which resembles the lacrimal gland in structure (Glandula superficialis palpebæ tertiæ).

Ordinarily the third eyelid extends very little over the inner end of the cornea, but when the eyeball is strongly retracted (as in tetanus) the membrana is protruded over it so as to measure about an inch (ca. 2 to 3 cm.) in its middle. This effect results from the pressure of the eyeball and its muscles on the fat which surrounds the deep part of the cartilage.

=Vessels and Nerves.=—The =arteries= which chiefly supply the eyelids and conjunctiva are branches of the ophthalmic and facial arteries, and the blood is drained away by corresponding veins. The =sensory nerves= are branches of the ophthalmic and maxillary divisions of the trigeminus. The =motor nerves= to the orbicularis oculi, corrugator supercilii, and malaris come from the facial nerve, the levator palpebræ superioris is innervated by the oculomotor, and the unstriped muscle of the lids by the sympathetic.

THE LACRIMAL APPARATUS

The =lacrimal apparatus= (Apparatus lacrimalis) comprises: (1) the lacrimal gland, which secretes the clear lacrimal fluid; (2) the excretory ducts of the gland; (3) the two lacrimal ducts or canaliculi, lacrimal sac, and naso-lacrimal duct, which receive the fluid and convey it to the nostril.

The =lacrimal gland= (Glandula lacrimalis) is situated between the supraorbital process and the dorso-lateral surface of the eyeball (Fig. 438). It is flattened, oval in outline, and measures about two inches (ca. 5 cm.) transversely and an inch or more (2.5 to 3 cm.) in the sagittal direction. Its upper face is convex and is related to the concave lower surface of the supraorbital process. The lower face is concave in adaptation to the eyeball, from which it is separated by the periorbita. The =excretory ducts= (Ductuli excretorii) are very small and are twelve to sixteen in number; they open into the outer part of the conjunctival sac along a line a little in front of the fornix conjunctivæ superior. In appearance and structure the gland resembles the parotid. It receives its blood-supply chiefly from the lacrimal artery. The sensory nerve is the lacrimal, and the secretory fibers are derived from the sympathetic.

The =puncta lacrimalia= are the entrances to the two lacrimal ducts. Each is a fine slit-like opening (about 2 mm. long), situated close behind the free edge of the lid and about a third of an inch (ca. 8 mm.) from the internal canthus. The =lacrimal ducts= (Ductus lacrimales), upper and lower, begin at the puncta and converge at the inner commissure to open into the =lacrimal sac=. The latter (Saccus lacrimalis) may be regarded as the dilated origin of the naso-lacrimal duct. It occupies the funnel-like origin of the bony lacrimal canal, and leads to the =naso-lacrimal duct= (Ductus naso-lacrimalis), which passes forward and a little downward along the outer wall of the frontal sinus and the nasal cavity and opens near the lower commissure of the nostril. Its length is about ten to twelve inches (ca. 25 to 30 cm.). In the first part of its course it is inclosed in the osseous lacrimal canal; further forward it lies in the lacrimal groove of the maxilla, covered at first by a plate of cartilage and then by the mucous membrane of the middle meatus. The terminal part lies in the inferior turbinal fold and opens on the skin of the floor of the nostril near the transition to mucous membrane. Accessory openings may occur a little further back.

The first part of the duct, about 6 to 7 mm. in diameter, extends in a gentle curve, convex dorsally, from the internal commissure toward a point just above the level of the infraorbital foramen. The second part (isthmus) is narrower (ca. 3 to 4 mm.); it extends forward and a little ventrally about to a transverse plane through the first cheek tooth and lies in the groove above the inferior turbinal crest. Beyond this the duct inclines upward and widens very considerably, crosses the nasal process of the premaxilla obliquely, and contracts at its termination. The mucous membrane may present valvular folds, the most distinct of which is situated at the origin.

THE PERIORBITA

The =periorbita= or ocular sheath is a conical fibrous membrane which incloses the eyeball with its muscles, vessels, nerves, etc. Its apex is attached around the optic and lacerated foramina, and its base is in part attached to the bony rim of the orbit, in part continuous with the fibrous layer of the lids. Its inner part, which is in contact with the orbital wall, is thin; incorporated with it beneath the root of the supraorbital process is the bar of cartilage around which the superior oblique muscle is reflected. The outer part is thicker, and is strengthened by an elastic band which is attached to the pterygoid crest and furnishes origin to the thin unstriped orbital muscle. A quantity of fat (Corpus adiposum extraorbitale) lies about the periorbita, and within it is the intraorbital adipose tissue (Corpus adiposum intraorbitale) which fills the interstices between the eyeball, muscles, etc.

THE ORBITAL FASCIÆ AND OCULAR MUSCLES (Figs. 438, 439, 555)

The straight muscles of the eyeball and the oblique muscles in part are inclosed in fibrous sheaths (Fasciæ musculares), formed by superficial and deep layers of fascia, which are united by intermuscular septa in the interstices between the muscles. The =superficial fascia= is thin; it blends in front with the fibrous layer of the eyelids and is attached behind around the optic foramen. The =deep fascia= consists anteriorly of two layers, one of which is continuous with the fibrous tissue of the lids, while the other is attached at the corneo-scleral junction.

The posterior part of the eyeball is covered by the =bulbar fascia= or capsule of Tenon (Fascia bulbi), so that between them a lymph space (Spatium interfasciale) is inclosed which communicates with the subdural space along the course of the optic nerve.

The =levator palpebræ superioris= muscle[217] is a thin band about half an inch in width which lies above the rectus superior. It is narrow at its origin above and behind the ethmoidal foramen and ends by an expanded tendon in the upper lid. Its action is to raise the upper lid.

The =recti oculi= (Mm. recti bulbi) are four in number and are designated according to their positions as =superior=, =inferior=, =internal=, and =external=. They are all band-like, arise close together around the optic foramen, and diverge as they pass forward to the eyeball. On reaching the latter they end in thin tendons which are inserted into the sclera in front of the equator of the eyeball.

The =retractor oculi= (M. retractor bulbi) surrounds the optic nerve, and is incompletely divided into four parts which alternate with the recti. They arise around the optic nerve and are inserted into the sclera behind the recti.

The =obliquus oculi superior= (M. obliquus bulbi dorsalis s. superior) is the longest and narrowest of the ocular muscles. It arises near the ethmoidal foramen and passes forward internal to the rectus internus. Under the root of the supraorbital process it is reflected almost at a right angle around a cartilaginous pulley (trochlea), which is attached to the anterior part of the inner wall of the orbit, a bursa being interposed here. The muscle is then directed outward and somewhat forward, and ends in a thin tendon which passes between the rectus superior and the eyeball, and is inserted into the sclera between the superior and external recti, about half an inch behind the margin of the cornea.

The =obliquus oculi inferior= (M. obliquus bulbi ventralis s. inferior) is wide and much shorter than the recti. It arises from the inner wall of the orbit in the small depression (Fossa muscularis) behind the lacrimal fossa. It curves around the rectus inferior and is inserted into the sclera near and partly beneath the rectus externus.

=Actions.=—The superior and inferior recti rotate the eyeball about a transverse axis, moving the vertex of the cornea upward and downward respectively. Similarly the internal and external recti rotate the eyeball about a vertical axis, turning the vertex of the cornea inward and outward respectively. The oblique muscles rotate the eyeball about a longitudinal axis; the superior oblique raises the outer end of the pupil, while the inferior oblique lowers it. The retractor as a whole draws the eyeball backward, and its parts may separately reinforce the corresponding recti. Also the four recti acting together will retract the eyeball.

The actual movements of the eyeball are by no means so simple as might be inferred from the foregoing general statements. Practically all movements are produced by the coördinated actions of several muscles, involving combinations which are quite complex and difficult to analyze accurately. Further complication is caused by the fact that the recti are not inserted at equal distances from the equator and the axes of rotation of the oblique muscles do not correspond to the longitudinal axis of the eyeball.

=Nerve-supply.=—The oculomotor nerve supplies the foregoing muscles, with the exception of the rectus externus and obliquus superior, which are innervated by the abducens and trochlearis respectively.

THE EYEBALL

The =eyeball= (Bulbus oculi) is situated in the anterior part of the orbital cavity, protected in front by the eyelids and conjunctiva, in its middle by the complete orbital ring, and related behind to the bulbar fascia, fat, and ocular muscles.

It has the form approximately of an oblate spheroid, but is composed of the segments of two spheres of different sizes. The anterior, transparent, corneal segment has a radius of curvature of about 17 mm., and the posterior, opaque, scleral segment a radius of about 25 mm. The anterior segment therefore projects more strongly, and the junction of the two segments is marked externally by a broad, shallow groove, the sulcus scleræ. The central points of the anterior and posterior curvatures of the eyeball are termed respectively the =anterior= and =posterior poles= (Polus anterior, posterior), and the line connecting the poles is the =optic axis= (Axis oculi externa). The angle of divergence of the optic axes is about 137 degrees. The =equator= (Æquator) is an imaginary line drawn around the eyeball midway between its poles, and =meridians= (Meridiani) are lines drawn around it through the poles.

The average transverse diameter of the eyeball is about 5 cm., the vertical about 4.5 cm., and the axial about 4.25 cm. The distance from the anterior pole to the point of entrance of the optic nerve is about 3 cm.

The eyeball consists of three concentric tunics or coats, within which three refractive media are inclosed.

THE FIBROUS TUNIC

The =fibrous tunic= (Tunica fibrosa oculi) is the external coat and is composed of a posterior opaque part, the sclera, and a transparent anterior part, the cornea.

The =sclera=, popularly termed the “white of the eye,” is a dense fibrous membrane which forms about four-fifths of the fibrous tunic. Thickest in the vicinity of the posterior pole (ca. 2 mm.), it thins at the equator (ca. 0.4 mm.), and increases in thickness toward the junction with the cornea (ca. 1.3 mm.). It is in general white, but may have a bluish tinge in its thinnest parts. Its external surface furnishes insertion to the ocular muscles and is covered by the conjunctiva scleræ in its anterior part. The episcleral tissue, which is richly supplied with vessels and nerves, attaches the conjunctiva to the sclera; it is abundant and loosely meshed except at the junction with the cornea. The inner surface is attached to the chorioid coat by a layer of delicate, pigmented, connective tissue, the =lamina fusca=. The anterior border is oval, the long axis being transverse, and is continuous with the cornea. The transition from the opaque scleral tissue to the transparent corneal substance occurs in such manner that the sclera appears to form a groove (Rima cornealis), into which the cornea fits somewhat as a watch-glass in the case. Near the corneo-scleral junction there is a circular venous plexus, the =plexus= s. =sinus venosus scleræ=, formerly called the canal of Schlemm. The optic nerve passes through the posterior part of the sclera a little below and external to the posterior pole. The opening for the nerve is crossed by interlacing fibrous strands, forming the =lamina cribrosa scleræ=.

The sclera consists of interlacing bundles of white fibrous tissue, associated with which there are a few elastic fibers. The bundles are arranged chiefly in meridional and equatorial layers. The very limited blood-supply is derived from the ciliary arteries, and the veins open into the venæ vorticosæ and ciliary veins. The lymphatics are represented by intercommunicating cell spaces. The nerves are derived from the ciliary nerves.

The =cornea= forms the anterior fifth of the fibrous tunic. It is transparent, colorless, and non-vascular. Viewed from in front it is oval in outline, the long axis being transverse and the broad end internal; it appears more nearly circular when viewed from behind. Its =anterior surface= (Facies anterior) is convex and is more strongly curved than the sclera; its central part is termed the =vertex corneæ=. The =posterior surface= (Facies posterior) is concave; it forms the anterior boundary of the anterior chamber, and is in contact with the aqueous humor. The margin (limbus corneæ) joins the sclera; the latter overlaps the cornea more in front than behind, and more above and below than at the sides, thus explaining the difference in outline of the two surfaces. The cornea is thinnest at the vertex.

The cornea consists, from before backward, of the following layers: (1) The =epithelium corneæ= is continuous with that of the conjunctiva scleræ, and is of the stratified squamous type. (2) The =lamina limitans anterior= is merely a condensation of the next layer. (3) The =substantia propria= forms the bulk of the cornea and is composed of interlacing bundles of connective tissue, arranged in part in lamellæ disposed parallel with the surface. In the amorphous cement substance between the lamellæ are flattened connective-tissue cells, the corneal corpuscles. These have branching processes which unite with those of other cells, thus forming a protoplasmic network.[218] (4) The =lamina elastica posterior=, also termed the membrane of Descemet or Demours, is a thin and practically homogeneous membrane which is less intimately attached to the substantia propria than the anterior lamina. It is clear, glistening, and elastic. At the periphery the lamina divides into three sets of fibers. The anterior fibers join the sclera, the middle give attachment to the ciliary muscle, while the posterior pass into the iris and form the =ligamentum pectinatum iridis=. (5) The =endothelium= (cameræ anterioris) consists of a layer of flattened polygonal cells, and is reflected on to the anterior surface of the iris.

The cornea is without =blood-vessels= except at its periphery, where the terminal twigs of the vessels of the sclera and conjunctiva terminate in loops. The =nerves= are derived from the ciliary nerves. They form a plexus around the periphery (Plexus annularis), from which fibers pass into the substantia propria, become non-medullated, and form the fundamental or stroma plexus. From this perforating branches pass through the anterior limiting layer and form a subepithelial plexus, from which filaments ascend between the epithelial cells. Other branches from the plexuses in the substantia propria end as fibrils which are in close relation with the corneal corpuscles.

THE VASCULAR TUNIC

The =vascular tunic= (Tunica vasculosa oculi) lies internal to the fibrous coat; it comprises three parts—the chorioid, the ciliary body, and the iris.

1. The =chorioid= (Chorioidea) is a thin membrane which lies between the sclera and retina. It is in general rather loosely attached to the sclera by the lamina fusca, but is intimately adherent at the point of entrance of the optic nerve and less closely in places where the ciliary vessels and nerves pass through. The inner surface is in contact with the layer of pigmented cells of the retina, which adhere so closely to the chorioid that they were formerly regarded as a part of the latter. The general color of the chorioid is dark brown, but an extensive semilunar area a little above the level of the optic papilla has a remarkable metallic luster, and is termed the =tapetum= of the chorioid (Tapetum chorioideæ). The appearance here varies in different individuals, but the prevailing colors in most cases are iridescent blue and green in various nuances shading into yellow. Posteriorly the chorioid is perforated by the optic nerve, and anteriorly it is continuous with the ciliary body.

The chorioid consists of four layers, which from without inward are as follows: (1) The =lamina suprachorioidea= consists of interlacing fine lamellæ of fibrous tissue, each containing a network of elastic tissue. Among these are large-branched, pigmented, connective-tissue cells. The spaces between the lamellæ are lined with endothelium, and form a system of lymph-clefts which together form the perichorioid space (Spatium perichorioideale). (2) The =lamina vasculosa= is the outer part of the proper tissue of the chorioid. It contains the larger blood-vessels, which are supported by connective-tissue and elastic fibers. (3) The =lamina choriocapillaris= consists of an extremely rich network of capillaries embedded in an almost homogeneous matrix. Between it and the lamina vasculosa is a layer of fibro-elastic tissue, the =tapetum fibrosum=, which causes the metallic luster mentioned above. (4) The =lamina basalis= is very thin and transparent. It is composed of an inner homogeneous part and an outer elastic part.

2. The =ciliary body= (Corpus ciliare), the middle part of the vascular coat, connects the chorioid with the periphery of the iris. In meridional section it has the form of a narrow triangle, the base of which is next to the iris. On its inner side are the ciliary processes and on its outer side the ciliary muscle. It consists of three parts—the ciliary ring, ciliary processes, and ciliary muscle. The =ciliary ring= (Orbicularis ciliaris) is the posterior zone, which is distinguished from the chorioid mainly by its greater thickness and the absence of the choriocapillaris. Its inner face presents numerous fine meridional ridges, by the union of which the ciliary processes are formed. The =ciliary processes= (Processus ciliares), more than a hundred in number, form a circle of radial folds which surround the lens and furnish attachment to the zonula ciliaris or suspensory ligament of the latter. They are small at their origin on the ciliary ring and become much thicker and higher toward their inner ends. The width of the circle formed by them is narrower at the inner side than elsewhere. Their bases extend forward to the periphery of the iris, and their inner ends are close to the margin of the lens. They bear numerous secondary folds. Their inner surface is covered by a continuation of the lamina basalis of the chorioid, on which there are two layers of epithelial cells which constitute the pars ciliaris retinæ. They consist of a rich network of tortuous vessels supported in pigmented connective tissue. The =ciliary muscle= (M. ciliaris) (Figs. 552, 555, 559) constitutes the outer part of the ciliary body, and lies between the sclera and the ciliary processes. It forms a circular band of unstriped muscle, the fibers of which are for the most part directed meridionally. They arise from the inner surface of the sclera and from the ligamentum pectinatum iridis close to the corneo-scleral junction, and run backward along the sclera to be inserted into the ciliary processes and ring. When the muscle contracts, it pulls the processes and ring forward, thus slackening the ciliary zone or suspensory ligament of the lens, and allowing the latter to become more convex. This is the mechanism of accommodation for near objects.

In man the muscle has the form of a prismatic ring which is triangular in meridional section, the base being directed toward the periphery of the iris. It consists chiefly of meridional fibers, but a ring of circular fibers forms the inner angle of its base. In the horse the muscle is much less developed, and has the form of a flat band; it does not contain circular fibers, but the arrangement is rendered more or less plexiform by the existence of oblique and equatorial fibers.

3. The =iris= (Figs. 552, 557, 559) is a muscular diaphragm placed in front of the lens, and is visible through the cornea. It is pierced centrally by an elliptical opening, the =pupil= (Pupilla), which varies in size during life and determines the amount of light admitted to act on the retina. In strong light the vertical diameter of the pupil is very short, but the opening is almost circular when the pupil is fully dilated. The =ciliary border= (Margo ciliaris) or periphery of the iris is continuous with the ciliary body and is connected with the corneo-scleral junction by the ligamentum pectinatum iridis. The ligament consists of strands of connective tissue which are attached externally to the corneo-scleral junction. Its bundles interlace and inclose spaces (Spatia anguli iridis) which are lined with endothelium and communicate with the anterior chamber. The =pupillary border= (Margo pupillaris) surrounds the pupil. Its upper part bears in its middle several black masses of variable size, termed the =granula iridis= or corpora nigra; similar, but much smaller, projections may be seen on the lower margin of the pupil. The =anterior surface= (Facies anterior) determines the color of the eye, which is dark brown usually. It is marked by delicate concentric lines (Plicæ iridis), which fade out near the pupil. The smooth, narrow, central part is termed the pupillary zone or annulus iridis minor, while the much broader plicated part is the ciliary zone or annulus iridis major. The =posterior surface= (Facies posterior) is usually black. It bears numerous fine radial lines except at the pupillary margin. Its central part is in contact with the anterior surface of the lens, but peripherally the two are separated by a narrow space termed the posterior chamber. The iris consists chiefly of the =stroma iridis=, a delicate framework of connective tissue, which supports numerous blood-vessels, and contains branched pigmented cells. The muscular tissue (unstriped) consists of a sphincter and a dilator of the pupil. The =sphincter pupillæ= lies in the posterior part around the pupil, with which the fibers are largely concentric. The =dilatator pupillæ= consists of fibers which radiate outward from the sphincter to the ciliary border. The anterior surface of the iris is covered by a continuation of the endothelium of the cornea. Beneath this is a condensation of the stroma, in which the cells are close together and are full of pigmented granules.[219] There appear to be minute clefts here by which the lymph-spaces of the stroma communicate with the anterior chamber. The posterior surface is covered by a pigmented epithelium, the stratum pigmenti iridis, which is a continuation of that of the ciliary body.

The =arteries= of the vascular tunic come from the ciliary branches of the ophthalmic artery. The arteries of the chorioidea are derived chiefly from the short posterior ciliary arteries. These perforate the sclera around the posterior pole, run forward in the lamina vasculosa, and form the rich capillary network of the choriocapillaris. The two long ciliary arteries perforate the sclera obliquely near the optic nerve; they run forward in the lamina suprachorioidea in the horizontal meridian, one on the inner, the other on the outer, side of the eyeball. On reaching the ciliary body each divides into diverging branches; the subdivisions of these unite with each other and with twigs of the anterior ciliary arteries to form a circular anastomosis, the =circulus arteriosus major=. From this branches go to the ciliary muscle and processes and to the iris. The two anterior ciliary arteries, dorsal and ventral, form an episcleral plexus around the corneo-scleral junction, and give off branches which perforate the sclera. These supply twigs to the ciliary muscle and recurrent branches to the chorioid, and assist in forming the circulus arteriosus major.

The blood is carried away from the vascular tunic chiefly by four or five venous trunks, the =venæ vorticosæ=, which are formed by the convergence in whorls of numerous veins, coming not only from the chorioid, but also from the ciliary body and iris. The venæ vorticosæ perforate the sclera about at the equator and join the veins of the ocular muscles.

The =nerves= come from the long and short ciliary nerves. They form a plexus in the lamina suprachorioidea, which contains ganglion cells, and sends numerous non-medullated fibers chiefly to the blood-vessels of the chorioid. At the ciliary muscle a second plexus (P. gangliosus ciliaris) is formed, which supplies the muscle and sends fibers to the iris. The sphincter pupillæ is supplied by fibers derived from the oculomotor nerve, while the dilatator pupillæ is innervated by the sympathetic.

THE RETINA

The =retina= or nervous tunic of the eyeball is a delicate membrane which extends from the entrance of the optic nerve to the margin of the pupil. It consists of three parts. The large posterior part, which alone contains the nervous elements, including the special neuro-epithelium and the optic nerve-fibers, is termed the =pars optica retinæ=. It extends forward to the ciliary body, where it terminates at an irregular line called the =ora serrata=. Here the retina rapidly loses its nervous elements, becomes much thinner, and is continued over the ciliary body and the posterior surface of the iris by two layers of epithelial cells. In the =pars ciliaris retinæ= the inner stratum is non-pigmented, while the outer layer is a direct continuation of the stratum pigmenti of the pars optica. In the =pars iridica retinæ= both are pigmented. In the dead subject the pars optica is an opaque, gray, soft membrane which can be stripped of the chorioid, leaving most of its outer pigmented layer on the latter. During life it is transparent, except as to its pigmented epithelium, and the reddish appearance of the fundus as viewed by the ophthalmoscope is caused by the blood in the network of the choriocapillaris. The entrance of the optic nerve forms a sharply defined, oval, light area, the =optic papilla= (Papilla nervi optici), situated about 15 mm. below the horizontal meridian and 3 to 4 mm. external to the vertical meridian. The central part of the papilla is slightly depressed (Excavatio papillæ n. optici).

The transverse diameter of the papilla is about 6 to 7 mm., and the vertical about 4 to 5 mm. It is commonly situated a little below the margin of the tapetum, but the latter may extend down somewhat on either side of the papilla. The lower margin is often indented a little. In inspection of the fundus with the ophthalmoscope numerous fine branches of the arteria centralis retinæ are seen radiating from the periphery of the papilla.

The optic nerve-fibers converge from all parts of the pars optica to the papilla, where they collect into bundles which traverse the lamina cribrosa of the chorioidea and sclera, and constitute the optic nerve. The =area centralis retinæ= is a round spot, 2 to 3 mm. in diameter, situated above and external to the optic papilla; it corresponds to the macula lutea of man, which is histologically more highly differentiated than the rest of the retina and is the area of most acute vision.

The =structure= of the retina is very complex. It consists of nervous elements which are supported in a peculiar sustentacular tissue, and are covered externally by a layer of pigmented epithelium (Stratum pigmenti retinæ). The nervous elements comprise a highly specialized neuro-epithelium, the rods and cones; ganglion cells, the axones of which form the optic nerve; and intermediate neurones. Ten layers may be recognized in sections microscopically.[220]

The =arteries= of the retina are derived from the arteria centralis retinæ and anastomotic branches from the short ciliary arteries. The arteria centralis enters the optic nerve a short distance behind the eyeball and runs in the axis of the nerve. The artery divides 2 to 3 mm. before reaching the papilla, and gives off thirty to forty branches which radiate in the posterior part of the retina and divide dichotomously into end-arteries. The anterior part of the retina is non-vascular. The veins accompany the arteries except in the capillary plexuses; their walls consist merely of a layer of endothelial cells, around which are a lymph-channel and sheath.

CHAMBERS OF THE EYE AND AQUEOUS HUMOR

The =anterior chamber= of the eye (Camera oculi anterior) is inclosed in front by the cornea and behind by the iris and lens (Figs. 552, 555, 557). It communicates through the pupil with the =posterior chamber= (Camera oculi posterior); this is a small annular space, triangular in cross-section, which is bounded in front by the iris, behind by the peripheral part of the lens and its ligament, and externally by the ciliary processes. The chambers are filled by the =aqueous humor= (Humor aqueus), a clear fluid which consists of about 98 per cent. of water, with a little sodium chlorid and traces of albumin and extractives. It is carried off chiefly through the spaces (of Fontana) in the zonula ciliaris or suspensory ligament of the lens into the plexus venosus scleræ.

REFRACTIVE MEDIA OF THE EYEBALL

The =vitreous body= (Corpus vitreum) is a semifluid transparent substance situated between the crystalline lens and the retina. In front it presents a deep cavity, the =fossa hyaloidea=, which receives the posterior surface of the lens. It consists of a framework of delicate fibrils, the =stroma vitreum=, the meshes of which are filled by the fluid =humor vitreus=. The surface is covered by a condensation of the stroma known as the membrana hyaloidea.

The =crystalline lens= (Lens crystallina) is a biconvex, transparent body, situated in front of the vitreous body and in partial contact with the posterior surface of the iris. Its periphery, the =æquator lentis=, is almost circular and is closely surrounded by the ciliary processes. The =anterior surface= (Facies anterior) is convex; it is bathed by the aqueous humor and is in contact with the iris to an extent which varies with the state of the pupil. The =posterior surface= (Facies posterior) is much more strongly curved than the anterior. It rests in the fossa of the vitreous body. The central points of the surfaces are the =anterior= and =posterior poles= (Polus anterior et posterior lentis), and the line which connects them is the axis of the lens (Axis lentis).

The transverse diameter of the lens is about 2 cm., the vertical diameter is slightly smaller, and the axis measures about 13 mm. The radius of curvature of the anterior surface is 13.5 mm., and of the posterior surface 9.5 to 10 mm. But the curvatures of its surfaces—especially that of the anterior—vary during life according as the eye is accommodated for near or far vision.

The =zonula ciliaris= (of Zinn) or suspensory ligament of the lens (Fig. 552) consists of delicate fibers (Fibræ zonulares) which pass in a meridional direction from the ciliary processes to the capsule of the equator of the lens. Many fibers cross each other, and the spaces between the fibers (Spatia zonularia) are filled with aqueous humor; they communicate with each other and with the posterior chamber.

The =substance= of the lens (Substantia lentis) is inclosed by a structureless, highly elastic membrane, the =capsule= of the lens (Capsula lentis), and consists of a softer =substantia corticalis=, and a dense central part, the =nucleus lentis=. The capsule is thickest on the anterior surface, and here it is lined by a layer of flat polygonal cells, the epithelium of the lens capsule. The lens substance, when hardened, is seen to consist of concentric laminæ arranged somewhat like the layers of an onion, and united by an amorphous cement substance. The laminæ consist of lens fibers, hexagonal in section, and of very different lengths. Faint lines radiate from the poles and indicate the edges of layers of cement substance which unite the groups of lens fibers. These lines, the =radii lentis=, are three in number in the fœtus and new-born, and form with each other angles of 120 degrees. On the anterior surface one is directed upward from the pole and the other two diverge downward; on the posterior surface one is directed downward and the others diverge upward. The developed lens has neither vessels nor nerves.

In the fœtus the lens is nearly globular, and is soft and pinkish in color. During part of fœtal life it is surrounded by a vascular network, the tunica vasculosa lentis. This is derived chiefly from a temporary vessel, the hyaloid artery, which is a continuation forward of the arteria centralis retinæ through the hyaloid canal that traverses the vitreous body. In old age the lens tends to lose its elasticity and transparency; it also becomes flatter and the nucleus especially grows denser.

THE EAR

The ear or organ of hearing (Organon auditus) consists of three natural divisions—external, middle, and internal.

THE EXTERNAL EAR

The =external ear= (Auris externa) comprises (1) the =auricula=, a funnel-like organ which collects the sound waves, together with its muscles, and (2) the =external auditory canal=, which conveys these waves to the tympanic membrane, the partition which separates the canal from the cavity of the middle ear.

The =auricula= or pinna is attached by its base around the external auditory canal in such a manner as to be freely movable. In the following description it will be assumed that the opening is directed outward and that the long axis is practically vertical. It has two surfaces, two borders, a base, and an apex. The convex surface or dorsum (Dorsum auriculæ) faces inward and is widest in its middle part; its lower part is almost circular in curvature, while above it narrows and flattens. The concave surface (Scapha) is the reverse of the dorsum; it presents several ridges which subside toward the apex. The anterior border is sinuous; it is largely convex, but becomes concave near the apex. It divides below into two diverging parts (crura helicis). The posterior border is convex. The apex is flattened, pointed, and curved a little forward. The base is strongly convex. It is attached to the external auditory process of the petrous temporal bone, and around this there is a quantity of fat. The parotid gland overlaps it below and externally. The structure of the external ear comprises a framework of cartilages (which are chiefly elastic), the integument, and a complicated arrangement of muscles.

The =conchal= or =auricular cartilage= (Cartilago auriculæ) determines the shape of the ear; its form can be made out without dissection, except below, where it is concealed by the muscles and the parotid gland. The basal part is coiled to form a tube, which incloses the cavity of the concha (Cavum conchæ). This part is funnel-shaped and curves outward and a little backward. Its internal (medial) surface is strongly convex, forming a prominence termed the =eminentia conchæ=. The lowest part of the internal margin bears a narrow, pointed prolongation, the =styloid process=. This process is about an inch long and projects downward externally over the annular cartilage; the guttural pouch is attached to its free end. Behind its base there is a foramen through which the auricular branch of the vagus passes.

The basal part of the posterior border is cut into by a notch, which separates two irregular quadrilateral plates. The upper plate (Tragus) is overlapped by the anterior border, and is separated from the adjacent part of the posterior border (Antitragus) by a notch (Incisura intertragica). The lower plate is curved to form a half ring and partly overlaps the anterior border and the annular cartilage. Behind the notch there is a foramen, which transmits the internal auricular artery and internal auricular branch of the facial nerve.

The =annular cartilage= (Cartilago annularis) is a quadrilateral plate, curved to form about three-fourths of a ring; its ends are a little less than half an inch (ca. 1 cm.) apart internally and are united by elastic tissue. It embraces the external auditory process and forms with the lower part of the conchal cartilage the cartilaginous part of the external auditory canal.

The =scutiform cartilage= (Cartilago scutiformis s. scutulum) is an irregular quadrilateral plate which lies on the temporal muscle in front of the base of the conchal cartilage. Its superficial face is slightly convex from side to side and its deep face is correspondingly concave. The anterior end is thin and rounded; the posterior part or base is wider and thicker, and its inner angle is prolonged by a pointed process half an inch or more in length. The cartilage moves very freely over the underlying parts.

The =external auditory canal= or =meatus= leads from the cavum conchæ to the tympanic membrane. It does not continue the general direction of the cavity of the concha, but extends inward, downward, and slightly forward. It consists of a cartilaginous part formed by the lower part of the conchal cartilage and the annular cartilage, and an osseous part formed by the external auditory process of the temporal bone. These are united by elastic membranes to form a complete tube. Its caliber diminishes from without inward, so that the lumen of the inner end is about half of that of the outer end.

The =skin= on the convex surface of the concha presents no special features; it is attached to the cartilage by a considerable amount of subcutaneous tissue except at the apex. The integument which lines the concave surface is intimately adherent to the cartilage and is relatively dark in color. There are three or four cutaneous ridges which run about parallel with the borders of the conchal cartilage, but do not extend to the apex or the cavum conchæ. The upper and marginal parts and the ridges are covered with long hairs, but between the ridges and below it is thin, covered sparsely with very fine hairs, and supplied with numerous sebaceous glands. In the external auditory canal the skin becomes thinner; in the cartilaginous part it is supplied with numerous large, coiled, =ceruminous glands= (Glandulæ ceruminosæ) and is sparsely covered with very fine hairs; in the osseous part the glands are small and few or absent and there are no hairs.

THE AURICULAR MUSCLES

The =auricular muscles= may be subdivided into two sets, viz., (a) extrinsic muscles, which arise on the head and adjacent part of the neck, and move the external ear as a whole, and (b) intrinsic muscles, which are confined to the auricula. In this connection the scutiform cartilage may be regarded as a sesamoid cartilage intercalated in the course of some of the muscles.

The =extrinsic muscles= are as follows:

1. The =scutularis= is a thin muscular sheet situated subcutaneously over the temporalis muscle. Its fibers arise from the zygomatic arch and the frontal and sagittal crests, and converge to the scutiform cartilage. It consists of three parts.

(a) The =fronto-scutularis= comprises temporal and frontal parts, which arise from the zygomatic arch and the frontal crest, and are inserted into the outer and anterior borders of the scutiform cartilage respectively.

(b) The =interscutularis= arises from the sagittal crest, over which it is in part continuous with the muscle of the opposite side. Its fibers converge to the inner border of the scutiform cartilage.

(c) The =cervico-scutularis= is not well defined from the preceding muscle. It arises from the occipital crest and is inserted into the inner border of the scutiform cartilage.

2. The =anterior auricular muscles= (Mm. auriculares nasales) are four in number.

(a) The =zygomatico-auricularis= arises from the zygomatic arch and the parotid fascia, and is inserted into the outer face of the base of the conchal cartilage under cover of the parotido-auricularis.

(b) The =scutulo-auricularis superficialis inferior= arises on the outer part of the superficial face of the scutiform cartilage and ends on the base of the conchal cartilage with the preceding muscle.

(c) The =scutulo-auricularis superficialis medius= arises from the posterior part of the deep surface of the scutiform cartilage and is inserted into the dorsum of the conchal cartilage, close to the lower part of its anterior border and above and behind the preceding muscle. It receives a slip from the cervico-scutularis.

(d) The =scutulo-auricularis superficialis superior= is a thin slip which is detached from the interscutularis over the inner border of the scutiform cartilage. It ends on the anterior aspect of the lower part of the dorsum of the conchal cartilage.

3. The =superior auricular muscles= (Mm. auriculares dorsales) are two in number.

(a) The =scutulo-auricularis superficialis accessorius= is a narrow band which is largely covered by the preceding muscle. It arises from the posterior prolongation and the adjacent part of the superficial face of the scutiform cartilage, and is inserted into the convex surface of the conchal cartilage internal to the preceding muscle, the two crossing each other at an acute angle.

(b) The =parieto-auricularis= is flat and triangular; it arises from the sagittal crest under cover of the cervico-scutularis, runs outward and a little backward, and is inserted by a flat tendon into the lower part of the convex surface of the concha under cover of the cervico-auricularis superficialis.

4. The =posterior auricular muscles= (Mm. auriculares caudales) are three in number.

(a) The =cervico-auricularis superficialis= is a thin triangular sheet. It is wide at its origin from the occipital crest and the adjacent part of the ligamentum nuchæ, and becomes narrower as it passes outward to be inserted into the inner side of the convex surface of the concha.

(b) The =cervico-auricularis profundus major= arises from the ligamentum nuchæ, partly beneath and partly behind the preceding muscle. It is directed outward and is inserted into the postero-external aspect of the base of the ear, partly under cover of the parotido-auricularis.

(c) The =cervico-auricularis profundus minor= arises under the preceding muscle and passes downward and outward to be inserted into the lowest part of the convex surface of the concha, partly under cover of the parotid gland.

5. The =parotido-auricularis= (s. M. auricularis inferior) is a ribbon-like muscle which lies on the parotid gland. It is thin and wide at its origin from the fascia on the lower part of the parotid gland and becomes somewhat narrower and thicker as it passes upward. It is inserted into the conchal cartilage just below the angle of junction of its borders.

6. The =deep auricular= or =rotator muscles= (M. auriculares profundis, rotatores auriculæ), two in number, are situated under the scutiform cartilage and the base of the concha and cross each other.

(a) The =scutulo-auricularis profundus major= is the strongest of the auricular muscles. It is flat and is about an inch wide. It arises from the deep face of the scutiform cartilage and passes backward to end on and below the most prominent part of the base of the concha (eminentia conchæ).

(b) The =scutulo-auricularis profundus minor= lies between the base of the concha and the preceding muscle, and is best seen when the latter is cut and reflected. It is flat and about an inch in length. It arises from the posterior part of the deep face of the scutiform cartilage and from the cervico-scutularis, and passes downward, backward, and outward to be inserted into the base of the concha under cover of the preceding muscle.

7. The =tragicus= or mastoido-auricularis is a small muscle which arises from the temporal bone just behind the external auditory process and from the annular cartilage; it passes upward to be inserted into the lower part of the anterior border of the conchal cartilage.

The =intrinsic muscles= are very small and of little importance. They are as follows:

1. The =antitragicus= consists of a few bundles which are attached to the conchal cartilage behind the junction of its two borders, and are partially blended with the insertion of the parotido-auricularis.

2. The =helicis= is a small muscle attached in a position opposite to the preceding on the anterior border of the conchal cartilage; it extends also into the depression between the two divisions of the border. It is in part continuous with the insertion of the parotido-auricularis.

3. The =verticalis auriculæ=[221] is a thin stratum of muscular and tendinous fibers which extends upward on the posterior surface of the concha from the eminentia conchæ.

=Actions.=—The base of the concha is rounded and rests in a pad of fat (Corpus adiposum auriculæ), so that the movements of the external ear resemble those of a ball-and-socket joint. It is noticeable that movements about the longitudinal and transverse axes are accompanied by rotation. When the ear is vertical or drawn forward (“pricked up”), the opening is usually directed forward; conversely, when the ears are “laid back,” the opening faces backward. These movements evidently result from the coördinated actions of several muscles which are very complex and cannot be discussed in detail here. The scutularis acting as a whole fixes the scutiform cartilage, so that the muscles which arise on the latter act efficiently on the concha. The anterior auricular muscles in general erect the ear and turn the opening forward. The interscutularis concurs in this action, causing adduction and a symmetrical position of the ears; it also acts directly on the conchal cartilage, since the scutulo-auricularis superficialis superior is in reality a conchal insertion of the interscutularis. The scutulo-auricularis superficialis accessorius draws the concha forward and turns the opening outward. The parieto-auricularis adducts the concha and inclines it forward. The cervico-auricularis superficialis is chiefly an adductor of the conchal cartilage, and directs the opening outward. The cervico-auricularis profundus major turns the opening outward and, acting with the parotido-auricularis, inclines the ear toward the poll. The cervico-auricularis profundus minor tends to direct the opening downward and outward. The parotido-auricularis draws the ear downward and backward, and acts with the cervico-auricularis profundus major in “laying back the ears”; the deep auricular muscles concur in these actions. The tragicus shortens the external auditory canal. The actions of the intrinsic muscles are inappreciable.

The =arteries= of the external ear are derived from the anterior auricular branch of the superficial temporal, the posterior or great auricular branch of the internal maxillary, and the anterior branch of the occipital artery.

The =motor nerves= to the muscles come from the auricular and auriculo-palpebral branches of the facial nerve and from the first and second cervical nerves. The sensory nerves are supplied by the superficial temporal branch of the mandibular nerve and the auricular branch of the vagus.

THE MIDDLE EAR

The =middle ear= (Auris media) or =tympanic cavity= (Cavum tympani) is a space in the tympanic and petrous parts of the temporal bone situated between the membrana tympani and the internal ear. It is a pneumatic cavity, which is lined by mucous membrane, and communicates with the pharynx and the guttural pouch by the Eustachian tube. It contains a chain of auditory ossicles by which the vibrations of the membrana tympani are transmitted to the internal ear.

The cavity consists of: (1) A main part or atrium, which lies immediately to the inner side of the membrana tympani; (2) the recessus epitympanicus, situated above the level of the membrane and containing the upper part of the malleus and the greater part of the incus; (3) a relatively large ventral recess in the bulla ossea.

The =external wall= (Paries membranacea) is formed largely by the thin =membrana tympani=, which closes the inner end of the external auditory canal, and thus forms the septum between the external and middle parts of the ear. The membrane is an oval disc, which slopes obliquely downward and inward at an angle of about 30 degrees with the lower wall of the external auditory canal. The circumference is attached in a groove (Sulcus tympanicus) in the thin ring of bone (Annulus tympanicus) which almost completely surrounds it. The handle of the malleus (the outermost of the auditory ossicles) is attached to the inner surface of the membrane and draws the central part inward, producing a slight concavity of the outer surface. The periphery is thickened, forming the annulus fibrosus. The membrana tympani consists of three layers. The external =cutaneous layer= (Stratum cutaneum) is a prolongation of the lining of the external auditory meatus. The middle =fibrous layer= or =membrana propria= includes two chief sets of fibers; the outer stratum (Stratum radiatum) consists of fibers which radiate from the handle of the malleus, while the inner stratum (Stratum circulare) is composed of circular fibers which are best developed peripherally. There are also branched or dendritic fibers in part of the membrane. The internal =mucous layer= (Stratum mucosum) is a part of the general mucous membrane which lines the tympanic cavity.

The =internal wall= of the tympanic cavity (Paries labyrinthica) separates it from the internal ear; it presents a number of special features. The =promontory= (Promontorium) is a distinct eminence near the center which corresponds to the first coil of the cochlea, and is marked by a faint groove for the superficial petrosal nerve. Above this is the =fenestra vestibuli= (s. ovalis), a reniform opening which is closed by the foot-plate of the stapes and its annular ligament. The =fenestra cochleæ= (s. rotundum) is situated below and behind the preceding; it is an irregularly oval opening and is closed by a thin membrane (Membrana tympani secundaria), which separates the tympanic cavity from the scala tympani of the cochlea.

The =anterior wall= (Paries tubaria) is narrow, and is pierced by the slit-like tympanic opening of the Eustachian tube. Above this and incompletely separated from it by a thin plate of bone is the semicanal for the tensor tympani muscle.

The =superior wall= or =roof= (Paries tegmentalis) is crossed in its inner part by the facial nerve; here the facial canal is more or less deficient ventrally, and the nerve is covered by the mucous membrane of the tympanum.

The =posterior wall= (Paries mastoidea) presents nothing of importance; a tympanic antrum and mastoid cells, such as are found behind the tympanic cavity proper in man and many animals, are not present in the horse.

The =inferior wall= or =floor= (Paries tympanica) is concave and thin. It is crossed by delicate curved ridges, which radiate from the greater part of the annulus tympanicus.

The =auditory ossicles= (Ossicula auditus) form a chain which extends from the outer to the inner wall of the cavity. They are named, from without inward, the =malleus=, the =incus=, the =os lenticulare=, and the =stapes=. The first is attached to the inner surface of the tympanic membrane and the last is fixed in the fenestra vestibuli.

The =malleus= or hammer, the largest of the ossicles, consists of a head, neck, handle, and two processes. The =head= (Capitulum mallei) is situated in the epitympanic recess. It is smooth and convex above and in front, and presents on its postero-internal aspect a concave facet for articulation with the body of the incus. The =neck= (Collum mallei) is the constricted part below the head; its inner surface is crossed by the chorda tympani. The =handle= (Manubrium mallei) is directed downward, inward, and a little forward from the neck, and is attached along its entire length to the membrana tympani. On its inner surface, near the upper end, there is a slight projection to which the tendon of the tensor tympani muscle is attached. The =long process= (Processus longus) is a pointed spicule which projects forward from the neck toward the petro-tympanic fissure. The =short process= (Processus brevis) is a slight projection of the outer side of the neck, and is attached to the upper part of the membrana tympani.

The =incus= or anvil is situated chiefly in the epitympanic recess. It may be said to resemble a bicuspid tooth with two divergent roots, and consists of a body and two processes. The =body= (Corpus incudis) articulates with the head of the hammer. The =long process= (Crus longum) projects downward from the body and then curves inward; its extremity has attached to it a small nodule of bone, the os =lenticulare=, which articulates with the head of the stapes. The =short process= (Crus breve) projects chiefly backward, and is attached to the wall of the recess by a small ligament.

The =stapes= or stirrup consists of a head, two crura, and a base. The =head= (Capitulum stapedis) is directed outward and articulates with the os lenticulare. The =crura=, anterior and posterior (Crus anterius, posterius), are directed inward from the head, and join the ends of the base. The =base= or foot-plate (Basis stapedis) occupies the fenestra vestibuli, to which it is attached. The space between the crura and the base is closed by a membrane.

The =articulations= and =ligaments= of the auditory ossicles comprise: (1) A diarthrodial joint between the head of the malleus and the body of the incus (Articulatio incudomalleolaris), inclosed by a capsule. (2) An enarthrosis between the os lenticulare and the head of the stapes (Articulatio incudostapedia), also surrounded by a capsule. (3) The base of the stapes is attached to the margin of the fenestra vestibuli by a ring of elastic fibers (Lig. annulare baseos stapedis). (4) Small ligaments attach the head of the malleus and the short crus of the incus to the roof of the epitympanic recess. (5) The axial ligament (of Helmholtz) attaches the neck of the malleus to a small projection (Spina tympanica anterior) above and in front of the annulus tympanicus.

The =muscles= of the auditory ossicles are two in number, viz., the tensor tympani and the stapedius. The =tensor tympani= arises from the upper wall of the osseous Eustachian tube, and ends in a delicate tendon which bends outward and is inserted into the handle of the malleus near its upper end. When it contracts, it draws the handle of the malleus inward and tenses the membrana tympani; it probably also rotates the malleus around its long axis. It is innervated by the motor part of the trigeminus through the otic ganglion. The =stapedius= arises from a small prominence (Eminentia pyramidalis) of the posterior wall of the tympanum, runs forward on the facial nerve, and is inserted into the neck of the stapes. Its action is to draw the head of the stapes backward and rotate the anterior end of the base outward, thus tensing the annular ligament. It is innervated by the facial nerve.

The =tympanic mucous membrane= (Tunica mucosa tympanica) is continuous with that of the pharynx and the guttural pouch through the Eustachian tube. It is thin, closely united with the underlying periosteum, and is reflected over the ossicles, ligaments, and muscles, the chorda tympani, and the facial nerve in the open part of the facial canal. It contains minute lymph nodules and small mucous glands (Glandulæ tympanicæ). The epithelium is in general columnar ciliated, but over the membrana tympani, ossicles, and promontory it is flattened.

The =artery= of the tympanum is the stylo-mastoid, a small vessel which arises from the posterior auricular branch of the internal maxillary artery. It enters the tympanum through the stylo-mastoid foramen, and forms a circle around the tympanic membrane. The =nerves= of the mucous membrane come from the tympanic plexus.

THE EUSTACHIAN TUBE

The =Eustachian= or =auditory tube= (Tuba auditiva [Eustachii]) extends from the tympanic cavity to the pharynx; it transmits air to the former and equalizes the pressure on the two surfaces of the membrana tympani. It is directed forward, downward, and slightly inward, and is four to five inches (ca. 10 to 12 cm.) in length. Its posterior extremity lies at the inner side of the root of the muscular process of the petrous temporal, and communicates with the anterior part of the tympanic cavity by the small slit-like =tympanic opening= (Ostium tympanicum tubæ auditivæ). For a distance of about a quarter of an inch (ca. 6 to 7 mm.) in front of this opening it is a complete tube, with a curved lumen which is little more than a capillary space. Further forward it has the form of a plate which widens anteriorly and is curved to inclose a narrow groove, that opens ventrally into an extensive diverticulum termed the guttural pouch. The =pharyngeal opening= (Ostium pharyngeum tubæ auditivæ) is situated on the postero-superior part of the lateral wall of the pharynx just below the level of the posterior nares. It is a slit, an inch or more (ca. 3 cm.) in length, which slopes downward and backward. It is bounded internally by the thin free edge of the tube, from the lower part of which a fold of mucous membrane (Plica salpingo-pharyngea) extends in the same direction on the lateral wall of the pharynx for a distance of a little more than an inch usually. The outer boundary of the opening is the lateral wall of the pharynx. The basis of the tube is a plate of fibro-cartilage (Cartilago tubæ auditivæ) which is firmly attached dorsally to the fibrous tissue which closes the foramen lacerum basis cranii, the temporal wing of the sphenoid, and the pterygoid bone.[222] On cross-section the cartilage (except at its tympanic end) is seen to consist of two laminæ which are continuous with each other above. The internal lamina (Lamina medialis) gradually widens toward the pharyngeal end, where it forms a broad valvular flap. This is convex internally, and its thin anterior edge forms the inner margin of the pharyngeal opening. Behind this the lamina has a thick free edge which projects ventrally from the roof of the guttural pouch. The external lamina (Lamina lateralis) is narrow and thin, and is related externally to the levator and tensor palati muscles, which are in part attached to it; it does not exist at the pharyngeal end of the tube. The mucous membrane of the tube is continuous behind with that of the tympanum and in front with that of the pharynx. On either side it is reflected to form a large diverticulum, the guttural pouch. It is covered with ciliated epithelium, and contains mucous glands and lymph nodules.

The pharyngeal opening appears to be closed ordinarily, but the tube opens during deglutition. This action is apparently produced by the part of the palato-pharyngeus muscle which is attached to the tube.

THE GUTTURAL POUCHES

The =guttural pouches=, right and left (Figs. 255, 256, 569), are large mucous sacs, each of which is a ventral diverticulum of the Eustachian tube (Diverticulum tubæ auditivæ); they are not present in the domesticated animals other than the equidæ. They are situated between the base of the cranium and the atlas above and the pharynx below. Medially they are in apposition in great part, but are to some extent separated by the intervening ventral straight muscles of the head. The anterior end is a small cul-de-sac which lies below the body of the presphenoid between the Eustachian tube and the median recess of the pharynx. The posterior extremity lies near or below the atlantal attachment of the longus colli. The pouch is related dorsally to the base of the cranium, the atlanto-occipital joint capsule, and the ventral straight muscles. Ventrally it lies on the pharynx and the origin of the œsophagus. Laterally the relations are numerous and complex. They comprise the pterygoid, levator palati, tensor palati, stylo-hyoideus, and digastricus muscles; the parotid and submaxillary glands; the external carotid, internal maxillary, and external maxillary arteries; the internal maxillary and jugular veins; the pharyngeal or guttural lymph glands; the glosso-pharyngeal, hypoglossal, and superior laryngeal nerves. The vagus, accessory, and sympathetic nerves, the superior cervical ganglion, the internal carotid artery, and the inferior cerebral vein are situated in a fold of the upper wall of the pouch. The pouch is reflected around the anterior border of the great cornu of the hyoid bone so as to clothe both surfaces of the upper part of the latter. It thus forms an outer compartment, which extends backward external to the great cornu and the occipito-hyoideus muscle; it is related externally to the parotid gland, the articulation of the jaw, the ascending part of the internal maxillary artery, the superficial temporal artery, and the facial nerve; dorsally it covers the mandibular nerve and its chief branches, and is attached to the styloid process of the conchal cartilage.

Each pouch communicates with the pharynx through the pharyngeal orifice of the Eustachian tube, and is in direct continuity with the mucous membrane of the latter.

The wall of the pouch is a delicate mucous membrane which is in general rather loosely attached to the surrounding structures. It is covered with ciliated epithelium and is supplied with mucous glands.

It is worthy of note that the pharyngeal orifice of the Eustachian tube is at such a level as to provide (in the ordinary position of the head) only an overflow outlet for the escape of fluid which may accumulate in the pouch. The two pouches are often unequal in size, and variations in regard to the distance which they extend backward are not uncommon. In one case, a small aged horse, the right pouch extended along the œsophagus about five inches (ca. 12 cm.) behind the ventral tubercle of the atlas, and the left one a little more than two inches (ca. 6 cm.). No pathological changes were apparent, and the condition was not recognizable externally. Cases of extreme size—so-called tympanites—of the pouches occur, and are apparently congenital defects. In a case in a yearling colt, the head of which was 24 inches long, the left pouch extended about 12 inches (ca. 30 cm.) behind the tubercle of the atlas, and had a capacity of six quarts. The anterior end formed a cul-de-sac about two inches (ca. 5 cm.) long between the Eustachian tube and levator palati internally and the internal pterygoid muscle externally.

THE INTERNAL EAR

The =internal ear= or =labyrinth= (Auris interna s. Labyrinthus) consists of two parts, viz.: (1) a complex membranous sac, which supports the auditory cells and the peripheral ramifications of the auditory nerve; (2) a series of cavities in the petrous temporal bone, which inclose the membranous part. The first is called the =membranous labyrinth=, and contains a fluid, the =endolymph=. The second is the =osseous labyrinth=. The two are separated by the =perilymphatic space=, which is occupied by a fluid termed the =perilymph=.

THE OSSEOUS LABYRINTH

The =osseous labyrinth= (Labyrinthus osseus) (Fig. 565) is excavated in the petrous temporal bone to the inner side of the tympanic cavity. It consists of three divisions: (1) a middle part, the =vestibule=; (2) an anterior one, the =cochlea=; and (3) a posterior one, the =semicircular canals=.

1. The =vestibule= (Vestibulum) is the central part of the osseous labyrinth, and communicates in front with the cochlea, behind with the semicircular canals. It is a small, irregularly ovoid cavity, which is about 5 to 6 mm. in length. Its outer wall separates it from the tympanic cavity, and in it is the =fenestra vestibuli=, which is occupied by the base of the stapes. The inner wall corresponds to the fundus of the internal auditory meatus. It is crossed by an oblique ridge, the =crista vestibuli=, which separates two recesses. The anterior and smaller of these is the =recessus sphæricus=, which lodges the saccule of the membranous labyrinth. In its lower part there are about a dozen minute foramina which transmit filaments of the vestibular nerve to the saccule. The posterior and larger depression is the =recessus ellipticus=, which lodges the utricle of the membranous labyrinth. The crista vestibuli divides below into two divergent branches, which include between them the small =recessus cochlearis=; this is perforated by small foramina, through which nerve-bundles reach the ductus cochlearis. Similar foramina in the recessus ellipticus and the crista vestibuli transmit nerve filaments to the utricle and the ampullæ of the superior and external semicircular ducts. The anterior wall is pierced by an opening which leads into the scala vestibuli of the cochlea. The posterior part of the vestibule presents the four openings of the semicircular canals. The inner opening of the =aquæductus vestibuli= is a small slit behind the lower part of the crista vestibuli. The aquæductus passes backward in the petrous temporal bone, and opens on the inner surface of the latter near the middle of its posterior border; it contains the ductus endolymphaticus.

2. The =osseous semicircular canals= (Canales semicirculares ossei), three in number, are situated behind and above the vestibule. They are at right angles to each other, and are designated according to their positions as superior, posterior, and external. They communicate with the vestibule by four openings only, since the inner end of the superior and the upper end of the posterior canal unite to form a common canal (Crus commune), and the ampullate ends of the superior and external canals have a common orifice. Each canal forms about two-thirds of a circle, one end of which is enlarged and termed the =ampulla=. The =superior canal= (Canalis semicircularis superior) is nearly vertical and is placed obliquely with regard to a sagittal plane, so that its outer limb is further forward than the inner one. The antero-external end is the ampulla and opens into the vestibule with that of the external canal. The opposite non-dilated end joins the adjacent end of the posterior canal to form the crus commune, which opens into the supero-internal part of the vestibule. The =posterior canal= (Canalis semicircularis posterior) is also nearly vertical. Its ampulla is below, and opens into the vestibule directly, while the non-dilated end joins that of the superior canal. The =external canal= (Canalis semicircularis lateralis) is nearly horizontal. Its ampulla is external and opens into the vestibule with that of the superior canal.

3. The =cochlea= is the anterior part of the bony labyrinth. It has the form of a short blunt cone, the =base= of which (Basis cochleæ) corresponds to the anterior part of the fundus of the internal auditory meatus, while the =apex= or =cupola= (Cupula) is directed outward, forward, and downward. It measures about 7 mm. across the base and about 4 mm. from base to apex. It consists of a =spiral canal= (Canalis spiralis cochleæ), which forms two and a half turns around a central column termed the =modiolus=. The modiolus diminishes rapidly in diameter from base to apex. Its base (Basis modioli) corresponds to the area cochleæ of the fundus of the internal auditory meatus, and its apex extends nearly to the cupola. Projecting from the modiolus like the thread of a screw is a thin plate of bone, the =lamina spiralis ossea=. This begins between the two fenestræ and ends near the cupola as a hook-like process (Hamulus laminæ spiralis). The lamina extends about half-way to the periphery of the cochlea and partially divides the cavity into two passages; of these, the upper one is termed the =scala vestibuli=, and the lower the =scala tympani=. The membrana basilaris extends from the free margin of the lamina to the outer wall of the cochlea and completes the septum between the two scalæ, but they communicate through the opening (Helicotrema) at the cupola. The modiolus is traversed by an axial canal which transmits the nerves to the apical coil, and by a spiral canal (canalis spiralis modioli), which follows the attached border of the lamina spiralis, and contains the spiral ganglion and vein. Close to the beginning of the scala tympani is the inner orifice of the =aquæductus cochleæ=, a small canal which opens behind the internal auditory meatus, and establishes a communication between the scala tympani and the subarachnoid space.

The =internal auditory meatus= has been described in part (vide Osteology). The fundus of the meatus is divided by a ridge (Crista transversa) into upper and lower parts. The anterior part of the upper depression (Area n. facialis) presents the cranial opening of the facial canal; and the posterior part (Area vestibularis superior) is perforated by foramina for the passage of nerves to the utricle and the ampullæ of the superior and external membranous semicircular canals. The anterior part of the inferior depression (Area cochleæ) presents a central foramen and a spiral tract of minute foramina (Tractus spiralis foraminosus) for the passage of nerves to the cochlea. Behind these is an area of small openings which transmit nerves to the saccule (Area vestibularis inferior), and a single foramen (F. singulare) for the passage of a nerve to the ampulla of the posterior semicircular canal.

THE MEMBRANOUS LABYRINTH

The =membranous labyrinth= (Labyrinthus membranaceus) lies within, but does not fill, the osseous labyrinth. It is attached to the latter by delicate trabeculæ which traverse the perilymphatic space. It conforms more or less closely to the bony labyrinth, but consists of four divisions, since the vestibule contains two membranous sacs—the utricle and saccule.

1. The =utricle= (Utriculus), the larger of the two sacs, lies in the postero-superior part of the vestibule, largely in the recessus ellipticus. It receives the openings of the membranous semicircular canals, and the small =ductus utriculo-saccularis= leads from its lower part to the ductus endolymphaticus.

2. The =saccule= (Sacculus) is situated in the recessus sphæricus of the vestibule. From its lower part the =ductus reuniens= proceeds to open into the ductus cochlearis, a little in front of the blind end of the latter. A second narrow tube, the =ductus endolymphaticus=, passes from the posterior part of the saccule, and is joined by the ductus utriculo-saccularis; it then traverses the aquæductus vestibuli, and terminates under the dura mater on the posterior part of the internal surface of the petrous temporal bone in a dilated blind end, the saccus endolymphaticus.

3. The =membranous semicircular canals= (Ductus semicirculares) correspond in general to the osseous canals already described, but it may be noted that while the ampullæ of the membranous canals nearly fill those of the osseous canals, the other parts of the membranous canals only occupy about one-fourth of the bony cavities.

4. The =cochlear duct= (Ductus cochlearis) is a spiral tube situated within the cochlea. It begins by a blind end (Cæcum vestibulare) in the cochlear recess of the vestibule, and ends by a second blind end (Cæcum cupulare), which is attached to the cupola of the cochlea. The vestibular part is connected with the saccule by the ductus reuniens. The duct is triangular in cross-section, and it is usual to regard it as having three walls. The vestibular wall or roof, which separates the cochlear duct from the scala vestibuli, is formed by the very delicate =membrana vestibularis= (of Reissner), which extends obliquely from the lamina spiralis ossea to the outer wall of the cochlea. The tympanic wall or floor intervenes between the cochlear duct and the scala tympani; it is formed by the periosteum of the marginal part of the lamina spiralis and the =membrana basilaris=, which stretches between the free edge of the lamina and the outer wall of the cochlea. The outer wall consists of the fibrous lining of the cochlea, which is greatly thickened to form the =ligamentum spirale cochleæ=.

=Structure.=[223]—The membranous labyrinth consists in general of an outer thin fibrous layer, a middle transparent tunic, and an internal epithelium, composed of flattened cells. But in certain situations special and remarkable structures occur, among which are the following: (1) The =maculæ acusticæ= appear as small whitish thickenings of the inner walls of the saccule and utricle. The epithelium here consists of two kinds of cells, viz., supporting cells and hair cells. The latter are flask-shaped and are surrounded by the fusiform supporting cells. The free end of each hair cell bears a stiff, hair-like process composed of a bundle of cilia. Fibers of the saccular and utricular branches of the vestibular nerve form arborizations about the basal parts of the hair cells. Adherent to the surface of the maculæ are fine crystals of lime salts, embedded in a mucoid substance, and termed otoconia. (2) The =cristæ acusticæ= are linear thickenings of the wall of each ampulla of the membranous semicircular canals. Their structure is similar to that of the maculæ. (3) The =spiral organ of Corti= (Organon spirale) is an epithelial elevation which is situated upon the inner part of the membrana basilaris, and extends the entire length of the ductus cochlearis. It is very complicated in structure, but consists essentially of remarkable supporting cells and hair cells. Fibers of the cochlear nerve ramify about the basal parts of the hair cells.

=Vessels and Nerves.=—The =artery= of the internal ear is the internal auditory artery, a very small vessel which usually arises from the posterior cerebellar artery, and enters the internal auditory meatus. The =veins= go to the inferior petrosal sinus. The =vestibular nerve= is distributed to the utricle, saccule, and membranous semicircular canals, and mediates equilibration. The =cochlear nerve= gives a branch to the saccule and enters the central canal of the modiolus. Along its course it gives off fibers which radiate outward between the two plates of the lamina spiralis ossea, and ramify about the hair cells of the organ of Corti. The =ganglion spirale= or ganglion of Corti is situated in the spiral canal of the modiolus near the fixed border of the lamina spiralis. The cochlear nerve mediates the sense of hearing.

THE SKIN

The =skin= or =common integument= (Integumentum commune) is the protective covering of the body, and is continuous at the natural openings with the mucous membranes of the digestive, respiratory, and urogenital tracts. It contains peripheral ramifications of the sensory nerves, and is thus an important sense organ. It is the principal factor in the regulation of the temperature of the body, and by means of its glands it plays an important part in secretion and excretion. Some of its special horny modifications or appendages are used as organs of prehension or as weapons.

The =thickness= of the skin varies in the different species, on different parts of the body of the same animal, and also with the breed, sex, and age. The color also varies greatly, but this is masked in most places by the covering of hair or wool. The skin is in general highly elastic and resistant.

Permanent =folds= of the skin (Plicæ cutis) occur in certain situations, and in some places there are cutaneous =pouches= or =diverticula= (Sinus cutis).

The skin is attached to the underlying parts by the =subcutis= or =superficial fascia= (Tela subcutanea). This consists of connective tissue containing elastic fibers and fat. When the fat forms a layer of considerable thickness, it is termed the =panniculus adiposus=. Over a considerable part of the body the subcutis contains striped muscle, the =panniculus carnosus= (M. cutaneus); in some regions the fibers of the muscle are inserted into the skin, and their contraction twitches the skin or produces temporary folds.[224] The amount of subcutaneous tissue varies widely; in some places it is abundant, so that the skin can be raised considerably; in other situations it is practically absent and the skin is closely adherent to the subjacent structures. =Subcutaneous bursæ= often develop over prominent parts of the skeleton where there is much pressure or friction.

=Structure.=—The integument consists of the cutis or skin proper and its epidermal appendages, e. g., hairs, hoofs, claws, horns, etc. The cutis consists of two distinct strata, viz., a superficial epithelial layer, the =epidermis=, and a deep connective-tissue layer, the =corium=.

The =epidermis= is a non-vascular, stratified epithelium of varying thickness. It presents the openings of the cutaneous glands and the hair-follicles, and its deep surface is adapted to the corium.[225] It is divisible into a superficial, harder, drier part, the =stratum corneum=, and a deeper, softer, moister part, the =stratum germinativum=. The cells of the latter contain pigment, and by their proliferation compensate the loss by desquamation of the superficial part of the stratum corneum. In many places further subdivision into strata is evident on properly prepared cross-sections.

The =corium= consists essentially of a feltwork of connective-tissue and elastic fibers. It is well supplied with vessels and nerves, and contains the cutaneous glands, the hair-follicles, and unstriped muscle. The deeper part of the corium, the =tunica propria=, consists of a relatively loose network of coarse bundles of fibers, and in most places there is no clear line of demarcation between it and the subcutis. The superficial part, the =corpus papillare=, is of finer texture and is free from fat. Its superficial face is thickly beset with blunt conical prominences, the =papillæ=, which are received into corresponding depressions of the epidermis. They contain vascular loops and nerves, or, in certain situations, special nerve-endings.

The papillæ are best developed where the epidermis is thick and hairs are small or absent. On thickly-haired regions they are small or even absent. On certain parts of the body (anus, vulva, prepuce, scrotum, eyelids, etc.) the corium contains pigment in its connective-tissue cells.

The =glands= of the skin (Glandulæ cutis) are chiefly of two kinds, sudoriferous and sebaceous.

The =sudoriferous= or =sweat glands= (Glandulæ sudoriferæ) consist of a tube, the lower, secretory part of which is coiled in the deep part of the corium or in the subcutis to form a round or oval ball (Corpus glandulæ sudoriferæ). The excretory duct (Ductus sudoriferus) passes almost straight up through the corium, but pursues a more or less flexuous course through the epidermis, and opens into a hair-follicle or by a funnel-shaped pore (Porus sudoriferus) on the surface of the skin.

The =sebaceous glands= (Glandulæ sebaceæ) are in great part associated with the hairs, into the follicles of which they open. Their size varies widely, and is in general in inverse ratio to that of the hair. The larger ones are easily seen with the naked eye, and appear as small, pale yellow or brownish bodies. In certain situations (e. g., the labia vulvæ, anus, prepuce) they are independent of the hairs and are well developed. In form they may be branched alveolar, simple alveolar, or even tubular in type. They secrete a fatty substance, the =sebum cutaneum=, which serves as a protective against moisture, and may also (by its aromatic constituents) play an important part in the sexual life of animals.

The two kinds of glands described above are those which are most widely distributed, but many special types occur. Some of these are to be regarded as modified sweat glands, e. g., the naso-labial glands of the ox, the glands of the snout of the pig, and the glands of the plantar cushion of the horse. Others, e. g., the tarsal (or Meibomian) glands of the eyelids, are modified sebaceous. Still others are not yet classified satisfactorily. Some of these special types have been referred to in previous chapters, and others will receive attention in the special descriptions which follow. The mammary glands are highly modified cutaneous glands, which are intimately associated in function with the genital organs, and have been described with the latter.

=Vessels and Nerves.=—The =arteries= of the skin enter from the subcutis, where they communicate freely. In the deeper part of the corium they form a plexus, and another network is formed under the papillæ. Small vessels from the deep plexus go to the fat and sweat glands, and the subpapillary plexus sends fine branches to the papillæ, hair-follicles, and sebaceous glands. The =veins= form two plexuses, one beneath the papillæ, and another at the junction of the corium and subcutis. The =lymph vessels= form subpapillary and subcutaneous plexuses.

The =nerves= vary widely in number in different parts of the skin. The terminal fibers either end free in the epidermis and in certain parts of the corium, or form special microscopic corpuscles of several kinds.

THE APPENDAGES OF THE SKIN

The appendages of the skin are modifications of the epidermis, and comprise the hairs, hoofs, claws, horns, etc.

The =hairs= (Pili) cover almost the entire surface of the body in the domesticated mammals, and some parts which appear at first sight to be bare are found on close inspection to be provided with sparse and very fine hair. The hairs are constantly being shed and replaced, but at certain periods in the horse, for example, they fall out in great numbers, constituting the shedding of the coat. It is customary to distinguish the ordinary hairs (the coat), which determine the color of the animal, from the special varieties found in certain places. Among the latter are the long =tactile hairs= about the lips, nostrils, and eyes; the =eyelashes= or =cilia=; the =tragi= of the external ear; and the =vibrissæ= of the nostrils. Other special features will be noted in the discussion of the skin of the various species. The hairs are directed in such a way as to form more or less definite =hair-streams= (Flumina pilorum), and at certain points these converge to form =vortices= (Vortices pilorum).

The part of the hair above the surface of the skin is the =shaft= (Scapus pili), while the =root= (Radix pili) is embedded in a depression termed the =hair-follicle= (Folliculus pili). A vascular =papilla= (Papilla pili) projects up in the fundus of the follicle and is capped by the expanded end of the root, the =bulb= of the hair (Bulbus pili). The hair-follicles extend obliquely into the corium to a varying depth; in the case of the long tactile hairs they reach to the underlying muscle. Most of the follicles have attached to them small unstriped muscles known as the =arrectores pilorum=; these are attached at an acute angle to the under side of the deep part of the follicle, and their contraction causes erection of the hair and compression of the sebaceous glands, one or more of which open into the follicle.

The hairs are composed of epidermal cells, and consist from without inward of three parts. The =cuticle= is composed of horny, scale-like cells which overlap like slates on a roof. The =cortex= consists of horny fusiform cells which are packed close together and contain pigment. The =medulla= is the central core of softer, cubical or polyhedral cells; it contains some pigment and air-spaces.

The hair-follicles, being invaginations of the skin, are composed of a central epidermal part, and a peripheral layer which corresponds in structure to the corium. The follicles of the tactile hairs have remarkably thick walls which contain blood-sinuses between their outer and inner layers; in ungulates the sinuses are crossed by trabeculæ and assume the character of cavernous or erectile tissue.

The =hoofs=, =claws=, =horns=, and other horny structures consist of closely packed epidermal cells which have undergone cornification. In structure they might be compared to hairs matted together by intervening epidermal cells. They cover a specialized corium known as their =matrix=, from which the stratum germinativum derives its nutrition.

THE SKIN OF THE HORSE

The =thickness= of the skin of the horse varies from 1 to 5 mm. in different regions, and is greatest at the attachment of the mane and the ventral surface of the tail.

The =glands= are numerous and are larger than those of the other domesticated animals. The sebaceous glands are specially developed on the lips, the prepuce, mammary glands, perineum, and labia of the vulva. The sweat glands are yellow or brown in color. They occur in almost all parts of the skin, but are largest and most numerous on the outer wing of the nostril, the flank, mammary glands, and free part of the penis.

In addition to the ordinary and tactile =hairs= certain regions present coarse hairs of great length. The mane (Juba) springs from the dorsal border of the neck and the adjacent part of the withers; its anterior part, which covers the forehead to a variable extent, is termed the foretop (Cirrus capitis). The tail, with the exception of its ventral surface, bears very large and long hairs (Cirrus caudæ). The tuft of long hairs on the flexion surface of the fetlock (Cirrus pedis) gave rise to the popular name of this region.

The development of these special hairs varies widely, and is in general much greater in the draft breeds than in others. In Shire and Clydesdale horses, for instance, the hair on the volar aspect of the metacarpus and metatarsus and fetlock is often so long and abundant as to account for the term “feather,” which is commonly applied to it by horsemen.

THE HOOF

The =hoof=[226] (Unguis) is the horny covering of the distal end of the digit. It is convenient to divide it for description into three parts, termed the wall, sole, and frog.

1. The =wall= is defined as the part of the hoof which is visible when the foot is placed on the ground.[227] It covers the front and sides of the foot, and is reflected posteriorly at an acute angle to form the =bars=. The latter (Pars inflexa medialis, lateralis) appear on the ground surface of the hoof as convergent ridges, which subside in front and are fused with the sole; they are united with each other by the frog. For topographic purposes the wall may be divided into an anterior part or “toe” (Pars ungulæ dorsalis), lateral parts or “quarters” (Pars ungulæ medialis, lateralis), and the angles or “heels” (Pars ungularis medialis, laterales). It presents two surfaces and two borders.

The outer surface is convex from side to side and slopes obliquely from edge to edge. In front the angle of inclination on the ground plane is about 50° for the fore limb, 55° for the hind limb; on the sides the angle gradually increases and is 100° at the angles. The curve of the wall is wider on the external than on the internal side, and the external quarter is more oblique than the internal one. The surface is smooth and is crossed by more or less distinct ridges, which are parallel with the coronary border and indicate variations in the activity of the growth of the hoof. It is also marked by fine parallel striæ, which extend from border to border in an almost rectilinear manner.

The =slope= of the wall varies considerably in apparently normal hoofs. Lungwitz found by careful measurements of 56 fore and 36 hind feet the following average angles:

FORE FOOT HIND FOOT Toe 47.26° 54.1° Inner angle 101.57° 96.50° Outer angle 101.37° 96.1°

The wall of the fore foot may even be more upright than that of the hind, and may have an angle of 60°. The =length= of the wall at the toe, quarters, and heels is in the ratio of about 3 ∶ 2 ∶ 1 in the fore foot and about 2 ∶ 1½ ∶ 1 in the hind hoof.

The inner surface is concave from side to side, and bears about six hundred thin =primary laminæ= (Cristæ ungulæ), which extend from the coronary groove to the junction of wall and sole. Each bears a hundred or more =secondary laminæ= on its surfaces, so that the arrangement is pennate on cross-section. These horny laminæ are continued on the inner surface of the bars, and alternate with corresponding laminæ of the matrix.

The =proximal= or =coronary border= (Margo occultus) is thin. Its outer aspect is covered by a layer of soft horn known as the =periople=; this appears as a ring-like prominence above and gradually fades out below; at the angle it forms a wide cap or bulb and blends centrally with the frog. The inner aspect of the border is excavated to form the =coronary groove= (Sulcus coronalis ungulæ), which contains the thick coronary matrix. The groove is deepest in front, narrows on the sides, and is wide and shallow at the heels.[228] It is perforated by innumerable small, funnel-like openings which are occupied by the papillæ of the coronary matrix in the natural state.

The =distal= or =ground border= (Margo liber) of the unshod hoof comes in contact with the ground. Its thickness is greatest in front and decreases considerably from before backward on the sides, but there is a slight increase at the angles. Its inner face is united with the periphery of the sole by horn of lighter color and softer texture, which appears on the ground surface of the hoof as the =white line=.

In the case of horses at liberty the wall is usually worn off to the level of the adjacent sole, but if the ground is too soft the wall is likely to become unduly long and split or break or undergo deformation. On very hard or rough ground, on the other hand, the wear may be in excess of the growth. In the case of shod horses it is necessary to remove the excess of growth of the wall at each shoeing. The =thickness= of the wall at the toe, quarters, and heels is about in the ratio of 4 ∶ 3 ∶ 2 for the fore foot and about 3 ∶ 2½ ∶ 2 for the hind foot.

2. The =sole= (Solea ungulæ) forms the greater part of the ground surface of the hoof. It is somewhat crescentic in outline, and presents two surfaces and two borders.

The =superior= or =inner surface= is convex, and slopes with a varying degree of obliquity downward to the convex border. It presents numerous small funnel-like openings which contain the papillæ of the sole matrix in the natural state.

The =inferior= or =ground surface= is the converse of the preceding. It is normally arched—and more strongly in the hind than in the fore foot—but the curvature is subject to wide variation; in heavy draft horses the sole is commonly less curved than in the lighter breeds and may even be flat. The surface is usually rough, since the horn exfoliates here in irregular flakes.

The =convex border= is joined to the wall by relatively soft horn, previously referred to as forming the white line on the ground surface of the hoof. The angle of junction is rounded internally and presents a number of low ridges and specially large openings for the papillæ of the matrix. There is frequently a ridge of larger size at the toe.

The =concave border= has the form of a deep angle which is occupied by the bars and frog. By its junction with these it forms two pronounced ridges in the interior of the foot. The parts of the sole between the wall and bars may be termed its angles.

3. The =frog= (Furca ungulæ) is a wedge-shaped mass which occupies the angle between the bars and sole, and extends considerably below these on the ground surface of the foot. It may be described as having four surfaces, a base, and an apex.

The =superior= or =internal surface= is deeply concave from side to side. It bears a central ridge, the =spine= or “=frog-stay=” (Spina furcæ ungulæ), which is high posteriorly and subsides abruptly in front. On either side of this is a deep depression, bounded outwardly by the rounded ridge formed by the junction of the frog with the bar and sole. This surface presents fine striæ and openings for the papillæ of the frog matrix.

The =inferior= or =ground surface= presents a =central furrow= (Sulcus intercruralis), which is bounded by two ridges or crura (Crura furcæ ungulæ); these converge and form the apex.

The =sides= (Facies medialis et lateralis) are united at the upper part with the bars and sole, but are free below and form the central wall of the deep =lateral furrows= (Sulci cruroparietales), which are bounded outwardly by the bars.

The =base= is wide and high. It is depressed centrally and prominent at the sides, where it unites with the angles of the walls; the junction here is covered by the expanded periople and constitutes the bulb of the hoof.

The =apex= occupies the central angle of the concave border of the sole, and forms a blunt, round prominence a little in front of the middle of the ground surface of the hoof.

=Structure of the Hoof.=—The hoof is composed of epithelial cells which are more or less completely keratinized except in its deepest part, the =stratum germinativum=; here the cells have not undergone cornification, and by their proliferation maintain the growth of the hoof. The cells are in part arranged to form tubes which are united by intertubular epithelium, and inclose medullary cells and air-spaces.

The =wall= may be regarded as consisting of three layers. The external layer consists of the periople and the stratum vitreum. The =periople= is composed of soft, non-pigmented tubular horn. It is continuous with the epidermis above, and extends downward a variable distance. Usually it forms a distinct band somewhat less than an inch wide, except at the heels, where it is much wider, and caps the angle of inflection of the wall proper. The =stratum vitreum= is a thin layer of horny scales which gives the wall below the periople its smooth, glossy appearance. The =middle= or =tubular layer= forms the bulk of the wall, and is the densest part of the hoof. Its horn tubes run in a straight direction from the coronary to the ground border. In dark hoofs it is pigmented except in its deep part. The internal or laminar layer consists of the =primary= and =secondary laminæ= and is non-pigmented. The laminæ are narrow and thin at their origin at the lower margin of the coronary groove, but become wider and thicker below. At the junction of the wall and sole they are united by interlaminar horn to form the white line. Only the central part of the laminæ becomes fully keratinized. They are composed of non-tubular horn in the normal state.

The =sole= consists of tubular and intertubular horn. The tubes run parallel with those of the wall and vary much in size.

The =frog= is composed of relatively soft horn, which is much more elastic than that of the wall or sole, and is not fully keratinized. The horn tubes in it are slightly flexuous.

The hoof is non-vascular and receives its nutrition from the matrix. It is also destitute of nerves.

THE MATRIX OF THE HOOF

The =matrix= of the hoof (Matrix ungulæ) is the specially modified and highly vascular part of the corium of the common integument which furnishes nutrition to the hoof. It is convenient to divide it into five parts which nourish corresponding parts of the hoof.

1. The =perioplic matrix= or =ring= (Margo matricis ungulæ) is a band 5 to 6 mm. in width which lies in a groove between the periople and the coronary border of the wall. It is continuous above with the corium of the skin, and is marked off by a groove from the coronary matrix. At the heels it widens and blends with the matrix of the frog. It bears very fine, short papillæ which curve downward and are received in depressions of the periople, to which it supplies nutrition.

2. The =coronary matrix= or =cushion= (Corona matricis ungulæ) is the thick part of the corium which occupies the coronary groove, and furnishes nutrition to the bulk of the wall. It diminishes in width and thickness posteriorly, and along the upper border of the bar it is not very clearly defined from the matrix of the frog. The convex superficial surface is thickly covered with papillæ 4 to 6 mm. in length, which are received into the funnel-like openings of the coronary groove. At the heels and along the bars the papillæ are arranged in rows, separated by fine furrows. The deep surface is attached to the extensor tendon and the lateral cartilages by an abundant subcutis which contains many elastic fibers and a rich venous plexus.

3. The =laminar matrix= (Latus matricis ungulæ)—also termed the sensitive laminæ—bears primary and secondary laminæ which are interleaved with the horny laminæ of the wall and bars in the natural state. It is attached to the wall surface of the third phalanx by a modified periosteum (Stratum periosteale) which contains a close-meshed network of vessels, and to the lower part of the lateral cartilages by a subcutis which contains a rich venous plexus. The laminæ are small at their origin above, become wider below, and end in several papillæ 4 to 5 mm. in length. The sensitive laminæ supply nutrition to the horny laminæ and to the interlaminar horn of the white line.

4. The =sole matrix= (Latus volare matricis ungulæ)—also termed the sensitive sole—corresponds to the horny sole, to which it supplies nutrition. It is often more or less pigmented and bears long papillæ, which are specially large along the convex border and at the angles. Centrally it is continuous with the matrix of the frog and bars. The deep surface is attached to the sole surface of the third phalanx by a modified and highly vascular periosteum.

5. The =frog matrix= (Furca matricis ungulæ)—also called the sensitive frog—is moulded on the deep surface of the frog and bears small papillæ. Its deep face is blended with the plantar cushion. The germinal cells of the frog derive their nutrition from this part of the matrix.

The =digital= or =plantar cushion= (Torus digitalis) is an important part of the elastic apparatus of the foot. It is a wedge-shaped mass which overlies the frog. It presents for description four surfaces, a base, and an apex. The =superior surface= faces upward and forward and is connected with the distal fibrous sheath of the deep flexor tendon. The =inferior surface=, covered by the matrix of the frog, is moulded on the upper face of the frog. The =lateral surfaces= are related chiefly to the lateral cartilages; inferiorly the cushion is closely attached to the cartilages, but higher up a rich venous plexus intervenes. The =base=, situated posteriorly, is partly subcutaneous, and is divided by a central depression into two rounded prominences termed the bulbs of the plantar cushion. The =apex= lies under the terminal part of the deep flexor tendon. The cushion is poorly supplied with vessels. It consists of a feltwork of fibrous trabeculæ and elastic fibers, in the meshes of which are masses of fat. The bulbs are soft and loose in texture and contain a relatively large amount of fat, but toward the apex the cushion becomes denser and more purely white fibrous in structure. Branched =coil glands= occur chiefly in the part of the cushion which overlies the central ridge of the frog. Their ducts pursue a slightly flexuous course through the matrix and pass in a spiral manner through the frog. Their secretion contains fat.

=Vessels and Nerves.=—The matrix is richly supplied with blood by the =digital arteries=. The =veins= are valveless, and form remarkable plexuses which communicate freely with each other and are drained by the digital veins. The =lymph vessels= form subpapillary plexuses in the matrix of the sole and frog, and a wider-meshed plexus at the base of the plantar cushion. A considerable lymph vessel lies in the attached edge of each of the laminæ. The =nerves= are branches of the digital nerves; some fibers end in lamellar corpuscles and end-bulbs.

The =ergot= is a small mass of horn which is situated in the tuft of hair at the flexion surface of the fetlock. It is the vestige of the second and fourth digits of extinct equidæ and hence is absent in cases in which these digits are developed. A small tendinous band, 3 to 5 mm. in width, extends downward and slightly forward from the fibrous basis of the ergot on each side, crosses over the digital vessels and nerves very obliquely, and blends below with the digital fascia and the plantar cushion. It is known as the ligament or tendon of the ergot.

The term =chestnut= is applied to the masses of horn which occur on the inner surface of the forearm about a handbreadth above the carpus, and on the lower part of the inner face of the tarsus. They have an elongated oval form and are flattened. They are regarded usually as vestiges of the first digit. That of the hind limb is absent in the donkey and very small in the mule.

These horny vestiges are quite variable in form and size and are correlated with the fineness or coarseness of the integument in general. The supracarpal chestnut is about 1½ to 2½ inches long, oval in outline, the proximal end being pointed; it overlies the flexor carpi internus at a quite variable distance above the carpus, and hence should not be used as a surgical landmark. The tarsal chestnut lies at a point behind the lower part of the internal lateral ligament of the hock. When well developed it is about 2 to 2½ inches long, broad below and produced above to form a long pointed end, with a short blunt anterior process. They are composed of horn somewhat like that of the frog.

ORGAN OF SMELL

The peripheral part of the olfactory apparatus or organ of smell (Organon olfactus) is that part of the nasal mucous membrane which was referred to in the description of the nasal cavity as the olfactory region; this (Regio olfactoria) is limited to the ethmoturbinals and the adjacent part of the superior turbinal and the septum nasi, in which the fibers of the olfactory nerve ramify. It is distinguished by its yellow-brown color, thickness, and softness. It contains characteristic tubular =olfactory glands= (of Bowman), which are lined by a single layer of pigmented cells, and a neuro-epithelium, the =olfactory cells=, the central processes of which extend as non-medullated fibers to the olfactory bulb.

The epithelium is non-ciliated and is covered by a structureless limiting layer. It consists essentially of three kinds of cells, supporting, basal, and olfactory. The supporting cells are of long columnar form above and contain pigment granules; below they taper and often branch, and their central processes unite with those of adjacent cells to form a protoplasmic network. The basal cells are branched and lie on a basement membrane. The olfactory cells are situated between the supporting cells; they have the form of long narrow rods, with an enlarged lower part which is occupied by the nucleus. The peripheral end pierces the limiting membrane and bears a tuft of fine hair-like cilia (olfactory hairs). A central process extends from the nucleated pole of the cell to the olfactory bulb as a non-medullated olfactory nerve-fiber.

The =vomero-nasal organ= (of Jacobson) lies along each side of the anterior part of the lower border of the septum nasi. It communicates with the nasal cavity through the naso-palatine canal. It consists of a tube of hyaline cartilage lined with mucous membrane; a small part of the latter along the inner side is olfactory in character.

THE ORGAN OF TASTE

The peripheral part of the gustatory apparatus (Organon gustus) is formed by the microscopic =taste buds= (Calyculi gustatorii), which occur especially in the foliate, fungiform, and vallate papillæ, in the free edge and anterior pillars of the soft palate, and the oral surface of the epiglottis. The taste buds are ovoid masses, which occupy corresponding recesses in the ordinary epithelium; each presents a minute opening, the gustatory pore. The buds consist of fusiform supporting cells grouped around central =gustatory cells=. The latter are long and narrow; the peripheral end of each bears a small filament, the gustatory hair, which projects at the gustatory pore; the central end is produced to form a fine process which is often branched. The taste buds are innervated by fibers of the glosso-pharyngeal nerve and the lingual branch of the trigeminus.

SENSE ORGANS AND SKIN OF THE OX

THE EYE

The =eyelids= are thick, prominent, and less pliable than those of the horse. The lower lid bears a considerable number of cilia, which are, however, finer than those of the upper lid. The tarsal glands are more deeply embedded and therefore not so evident. The =conjunctiva= of the lower lid presents folds or ridges, and one or two prominences which contain numerous leukocytes; the conjunctival epithelium is transitional in type. The superficial part of the cartilage of the =third eyelid= is leaf or shovel-shaped and thicker than in the horse; the edge bears a narrower process, on which there is a transverse bar, giving the arrangement some resemblance to an anchor. The =gland= of the third eyelid is very large—an inch or more in length—and may be divided into two parts. The deep part is pink and consists of loose lobules, but the much larger superficial part is more compact. There are two large and several smaller excretory ducts. The subconjunctival tissue of the third eyelid contains lymph nodules, which are specially numerous on the bulbar side.

The =lacrimal gland= is thick and distinctly lobulated. It is more or less clearly divided into a thick upper and a thinner lower part (Glandula lacrimalis superior, inferior). There are six to eight larger excretory ducts and several smaller ones. The =naso-lacrimal duct= is shorter than in the horse, and is almost straight. Its terminal part is inclosed between two plates of cartilage, and it opens near the nostril on the outer wall; the orifice is placed on the inner side of the alar fold of the inferior turbinal, and is therefore not easily found.

The =eyeball= resembles that of the horse in shape, but is considerably smaller.

The average transverse diameter is about 42 mm., the vertical diameter 41 mm., and the axis 36 mm. The angle between the axes is about 119°.

The =sclera= is often more or less pigmented; where non-pigmented it may have a bluish tinge. The point of entrance of the optic nerve is about 2 mm. external to the vertical meridian, and about 7 mm. below the horizontal meridian.

The thickness of the sclera is about 2 mm. at the posterior pole, 1 mm. at the equator, and 1.2 to 1.5 mm. near the cornea.

The =cornea= is thicker than that of the horse.

The =tapetum= of the chorioidea is extensive at the outer side, but is a narrow strip internally. It has a metallic luster, shading from a brilliant green to a deep blue; centrally it has a reddish sheen.

The =iris= is usually very dark colored. The granula form a continuous series of small nodules along the upper margin of the pupil and are most prominent centrally; they are very small on the lower margin.

The =optic papilla= is much smaller and is not so sharply defined on ophthalmoscopic examination as that of the horse. Several relatively large retinal arteries radiate from the center of the papilla to the periphery of the retina. They may be seen to wind spirally around the veins, which are very large.

The arteria centralis retinæ arises from a posterior ciliary artery and divides close to the optic papilla into three branches usually; of these the upper is larger than the two lateral branches. The retina is more vascular than that of the horse; it has a round area centralis at the inner side, which is continued outward by a narrow strip of a similar histological structure.

The =vitreous body= is less fluid than that of the horse.

THE EAR

The =external ear= is inclined outward. The middle part is much wider and less curved than in the horse. The apex is also wide and does not curve forward. The lower part of the anterior border is bent backward and bears long hairs. The posterior border is thin and is regularly convex, except below, where it is indented. The opening is wide and the concave surface presents four ridges; the convex surface presents corresponding depressions. The styloid process of the conchal cartilage is short and blunt. The edges of the annular cartilage are in contact at the inner side and the upper border is notched externally. The scutiform cartilage is a very irregular quadrilateral plate; it is situated on the lateral aspect of the cranium with its concave surface in contact with the fat and temporalis muscle. The osseous external auditory meatus is directed practically straight inward; it is about twice as long as that of the horse, and tapers very gradually from without inward. The chief special characters of the =auricular muscles= are as follows: (1) The scutularis blends with the frontalis muscle. The interscutularis arises from the base of the processus cornu (or the corresponding area in polled cattle) and from the frontal crest. (2) The cervico-scutularis arises from the posterior surface of the cranium below the frontal eminence, and receives slips from the parieto-auricularis and cervico-auricularis superficialis. (3) The zygomatico-auricularis and scutulo-auricularis superficialis inferior are fused. (4) The scutulo-auricularis superficialis superior is distinct from the interscutularis; it arises from the superficial face of the scutiform cartilage. (5) The cervico-auricularis superficialis arises from the ligamentum nuchæ and ends on the convex surface of the conchal cartilage. (6) The parieto-auricularis arises from the nuchal surface of the frontal bone, the adjacent part of the parietal bone, and the ligamentum nuchæ; it is inserted below the preceding muscle. (7) The scutulo-auricularis superficialis accessorius arises from the superficial face of the scutiform cartilage and is inserted by a round tendon into the anterior part of the convex surface of the conchal cartilage. (8) The cervico-auricularis profundus minor consists of two fasciculi; the inner, narrow part is deep red in color, and arises from the fascia of the cervical muscles external to the occipital attachment of the ligamentum nuchæ; the outer, wider part is pale, and arises beneath the cervico-auricularis superficialis, indirectly from the scutiform cartilage. The two unite and are inserted into the lower aspect of the base of the conchal cartilage. (9) The scutulo-auricularis profundus minor arises from the temporal crest above the external auditory meatus and is inserted into the anterior part of the deep face of the scutiform cartilage.

The =cavum tympani= is small; it communicates ventrally with the air-cells of the bulla ossea. The tympanic membrane is nearly circular and is not so oblique as in the horse. The auditory ossicles are smaller than those of the horse; the malleus is more curved, the body of the incus is longer, and there is a small prominence on the front of the head of the stapes for the attachment of the stapedius muscle.

The =Eustachian tube= is small and is only about two inches long. The pharyngeal opening is small and is situated on the side of the fornix of the pharynx close to the base of the cranium. There is no flap-like expansion of the cartilage, but the inner border of the orifice is formed by a fold of mucous membrane.

The =internal ear= has essentially the same arrangement as in the horse.

COMMON INTEGUMENT

The thickness of the =skin= of the ox is greater than that of any of the other domesticated animals; in general it is about 3 to 4 mm., but at the root of the tail and the point of the hock it is about 5 mm. and on the brisket 6 to 7 mm. The variably developed prominence at the anterior part of the pectoral region known as the brisket consists of a fold of skin (Plica colli ventralis longitudinalis), which contains posteriorly a mass composed of coarse fibrous trabeculæ and fat.

The =cutaneous glands= are fewer and less developed than in the horse. Except about the natural openings, at the point of the hock, and the flexion surface of the fetlock, the =sweat glands= do not form a coil, but are enlarged at the deep end and are variably flexuous. The =sebaceous glands= are best developed about the natural openings and on the udder, but there are none on the teats. The =naso-labial glands= form a thick layer under the bare skin of the muzzle. They are compound tubular glands and are lined with cubical epithelium. The openings of their excretory ducts are easily seen.

The =hairs= are extremely variable in color and size in the different breeds and in different individuals. The hair of the frontal region is often curly, especially in the bull. There is no mane, and the long hairs of the tail occur only at the end, where they form the “brush” (Cirrus caudæ).

The =claws=, four in number on each limb, cover the ends of the digits. Those of the chief digits conform in a general way to the shape of the third phalanges, and each may be regarded as having three surfaces. The abaxial or outer surface is convex from side to side, and is marked by ridges parallel with the coronary border. Its anterior part is concave from edge to edge, and the angle which it forms with the ground is about 30°. The interdigital or inner surface is concave and grooved; it touches the opposite claw only at its ends. The inferior or ground surface consists of two parts, viz., a slightly concave sole, which is pointed in front and widens behind, and a prominent bulb of soft thin horn, which is continuous above with the skin. The claw may be regarded as consisting of three parts—periople, wall, and sole. The periople surrounds the coronary border in the form of a flat band, which is about half an inch wide, except at the heels, where it widens to cover the entire surface. The wall forms most of the abaxial or outer part of the claw and is reflected in front upon the interdigital surface. It thins out toward the bulb or heel, which appears, as stated above, to consist of the thin expansion of the periople. The sole occupies the angle of inflection of the wall; it is continuous without demarcation with the periople of the bulb. The perioplic matrix bears relatively long papillæ. The coronary matrix is much less developed than in the horse and its papillæ are short. The sensitive laminæ are much narrower and are more numerous than in the horse; secondary laminæ are not present. The matrix of the sole is not marked off behind from that of the periople; its papillæ are very small and close together. The matrix of the bulbs is separated from the flexor tendon by a mass of elastic, fatty tissue, which is analogous with the plantar cushion of the horse. The papillæ here are long and often compound.

The accessory digits bear short conical horn capsules which resemble in a general way those of the chief digits, and have a similar matrix, which covers one or two nodular vestigial phalanges. From these a fibrous band descends obliquely on the volar aspect of each chief digit and is attached below to the distal phalanx and sesamoid bones, sending fibers also to the elastic pad of the heel.

The =horns= (Cornua) inclose the horn processes of the frontal bones (except in the polled breeds). They vary very greatly in size, form, and curvature. The root or base of the horn (Radix cornus) has a thin edge which is continuous with the epidermis. It is covered by a thin layer of soft horn similar to the periople of the hoof of the horse. Near the root the horn is encircled by variable rings. Toward the apex (Apex cornus) the thickness of the horn increases till it becomes practically a solid mass. The horn consists mainly of tubes which are very close together, except at the rings, where there is more intertubular horn. The =matrix= of the horn (Matrix cornus) is united to the horn process by periosteum which is traversed by numerous blood-vessels. The matrix at the root of the horn is thick and bears long, slender papillæ; in the body of the horn it becomes thin and the papillæ are smaller, but increase in size apically. Rudimentary papillated laminæ also occur.

The =skin= of the =sheep= varies in thickness from 0.5 to 3 mm., but differs greatly in fineness and in other respects in various breeds. In Merinos considerable folds occur on the neck. Cutaneous pouches (Sinus cutis) are constantly present in certain situations. The =infraorbital= or =lacrimal pouch= (Sinus cutaneus infraorbitalis) is an invagination about half an inch in depth, which is situated in front of the inner angle of the eye. It bears scattered fine hairs, into the follicles of which large compound sebaceous glands open; coil glands are also present. The secretion of the glands is fatty and forms a yellow sticky covering on the skin when dry. The =inguinal= (or mammary) =pouch= (Sinus cutaneus inguinalis) is much more extensive, and is situated in the inguinal region in both sexes. The skin of the pouch bears scattered fine hairs and contains well-developed sebaceous glands and exceedingly large coil glands. The =interdigital pouch= (Sinus cutaneus interdigitalis) is a peculiar tubular invagination of the integument which opens at the anterior part of the interdigital cleft. On sagittal section it appears as a bent tube, an inch or more (ca. 2.5 to 3 cm.) in length, and about a fourth of an inch (ca. 6 to 7 mm.) in diameter. The pouch extends downward and backward, and then curves sharply upward between the distal ends of the proximal phalanges. Its deep blind end is somewhat ampullate. The subcutis forms a capsule around it. The skin of the pouch is thin and pale; it bears fine colorless hairs, the follicles of which receive the secretion of several sebaceous glands. The coil glands here are compound and very large; they open into the hair-follicles or directly into the pouch. The secretion of the glands is a colorless fatty substance. The skin is covered in great part by wool, which is similar in structure to hair, but is finer, curly, and usually contains no medullary cells. The follicles of the wool are curved, and are arranged more or less distinctly in groups of ten or a dozen, several of which open in common on the surface. A considerable part of the face and the limbs is covered with short, stiff hair, and long hairs occur more or less interspersed among the wool. The claws resemble those of the ox. The horns, when present, are more or less prismatic, distinctly ringed, and vary in length and curvature in different breeds. Their structure is similar to those of the ox.

The olfactory and gustatory organs resemble in general those of the horse.

SENSE ORGANS AND INTEGUMENT OF THE PIG

THE EYE

The posterior part of the orbital margin is formed chiefly by the orbital ligament, which extends from the extremely short supraorbital process to the small eminence at the junction of the malar and the zygomatic process of the temporal.

Cilia occur only on the upper eyelid. The inner canthus is prolonged by a groove on the infraorbital region. The tarsal glands are very short and curved. The conjunctival epithelium is of the transitional type with many goblet cells.

The deep part of the cartilage of the third eyelid is broad and spoon-like, the superficial part somewhat anchor-shaped. In addition to the gland which surrounds the deep part of the cartilage, there is a deeper gland of Harder (Glandula palpebræ tertiæ profunda), which is surrounded by a distinct capsule and a blood-sinus. This gland is brownish or yellowish-gray in color, elliptical in outline, and about an inch (2 to 3 cm.) in length. It is situated deeply below the attachment of the inferior oblique muscle.

The caruncula lacrimalis has the form of a ridge; it divides into two branches which join the skin at the inner commissure. It is red in color and contains numerous large coil glands.

The lacrimal gland is mucous in type. There is no lacrimal sac, and the two lacrimal ducts pass through separate openings at the infraorbital margin. The naso-lacrimal duct is usually short and opens into the inferior meatus at the posterior end of the inferior turbinal.[229]

The eyeball appears small, partly on account of the narrowness of the palpebral opening; it closely approaches the spherical form. The cornea, although in reality almost circular, appears oval when viewed from the front, the inner end being much the broader. The chorioid has no tapetum. The iris is usually dark grayish-brown or yellowish-brown, but sometimes has a blue tinge. The pupil is a transverse oval in ordinary light, but almost circular when dilated; granula are not present. The optic papilla is nearer the posterior pole than in the horse and ox, and has a distinct central artery and vein.

THE EAR

The external ear differs considerably in size, thickness, and position. It may be carried vertically, inclined inward, or hang downward. It is relatively wide and is little curved except at the base. The concave surface presents several cutaneous ridges which correspond approximately with the long axis of the ear. The anterior border of the concha is strongly recurved in its lower part, and divides into two branches, one of which passes almost horizontally backward in the cavum conchæ, while the other continues the general direction of the border. The posterior border is slightly concave above, strongly convex below, forming a prominence somewhat analogous to the lobule of the human ear. The osseous external auditory meatus is very long and is directed downward and inward. The tympanic membrane is almost circular.

The tympanic cavity proper is small, but it is continuous with the numerous cells of the large bulla ossea. The Eustachian tube is short; its pharyngeal opening is situated in the upper part of the wall of the pharynx immediately behind the posterior nares. It is somewhat infundibular, and is bounded internally by a thick fold of mucous membrane (Torus tubarius).

THE SKIN AND APPENDAGES

The thickness of the skin in improved breeds is 1 to 2 mm. Fat usually accumulates in the subcutis and forms a distinct and often extremely thick panniculus adiposus over the greater part of the body.

The sebaceous glands are in general small and much fewer than in the other animals. The sweat glands, on the other hand, are large, yellow or brownish in color, and are in many places visible to the naked eye. At the inner side of the carpus there are small cutaneous diverticula, the so-called carpal glands, into which numerous compound coil glands open. Large glands also occur in the skin of the digits and interdigital space. Compound tubular glands are present in the skin of the snout. Large sebaceous and sweat glands are found at the entrance to the preputial diverticulum.

The hairs are sparsely scattered in improved breeds—indeed, in some cases the skin is almost bare. The long hairs or bristles are arranged usually in groups of three. They are most developed on the neck and back. The bristles about the snout and the chin are sinus hairs.

The =claws= and their matrix resemble those of the ox, but the bulbs are more prominent and form a greater part of the ground surface; they are also better defined from the sole, which is small. The claws of the accessory digits are more developed and their parts better differentiated than those of the ox.

The olfactory region is extensive in correlation with the large size of the olfactory bulbs; the mucous membrane here is brown in color.

SENSE ORGANS AND INTEGUMENT OF THE DOG

THE EYE

The posterior margin of the orbit is formed by the orbital ligament, as in the pig. The orbital axes if produced backward would include an angle of about 79°, the optic axes an angle of about 92.5° (Koschel).

The lower eyelid has no distinct cilia. The inner angle is wide, the lacus lacrimalis shallow, and the caruncula lacrimalis small and yellowish-brown. The conjunctival epithelium is cylindrical, with many goblet cells. The gland which surrounds the deep end of the cartilage of the third eyelid is large and pink; it is a mixed gland.

The lacrimal gland is flat and lies chiefly under the orbital ligament. It is pink in color and mixed in structure. The naso-lacrimal duct is variable in arrangement and may differ on the two sides. It may open into the inferior meatus immediately after its emergence from the osseous lacrimal canal; thence it continues forward and opens on the lateral wall of the nostril below the inferior turbinal fold.

The eyeball is almost spherical and is relatively large, especially in the small breeds. The sclera is thick in the ciliary region, where it contains a well-developed venous plexus; in the vicinity of the equator it is thin, and the chorioid shows through it. The cornea is almost circular. The chorioid is richly pigmented, and presents a well defined =tapetum cellulosum=; this is somewhat triangular in outline and has a metallic luster. Its color is often golden green, shading to blue peripherally, but the blue tone may predominate, and in other cases it is mainly golden yellow or reddish-yellow. The appearance is due to several layers of peculiar flattened polygonal cells. The ciliary muscle is more developed than in the other species. The iris is commonly light or yellow brown, but not rarely has a blue tinge; the color often differs in the two eyes. The pupil is round; its edge is either smooth or bears minute round prominences. The retina presents a round area centralis external to the optic papilla. The latter is variable in outline; commonly it has the form of a triangle with the angles rounded off, but is often round or oval. Branches of the central vessels of the retina radiate from the middle of the papilla. The surfaces of the lens are not so strongly curved as in the other domestic animals, and there is little difference in the radius of curvature of the two surfaces.

THE EAR

The external ear differs greatly in size and form in the various breeds; in most it is relatively wide and thin and the greater part of it hangs down over the opening. The anterior border has a prominence (Spina helicis) at its lower part, and below this it divides into two branches (Crura helicis). One of these continues down to a blunt point, while the other turns in to the cavity of the concha. The posterior border forms a pouch below its middle, and is thick and rounded in its basal part. Here the conchal cartilage bears a pointed process (Processus uncinatus), which projects upward and backward. The outer wall of the cavum conchæ is supported by a quadrilateral plate (Tragus) above and a semiannular cartilage below. The concave surface presents several cutaneous folds, and in the cavum conchæ there are ridges and irregular prominences. There are long hairs on the borders, apex, and the folds of the concave surface, but the skin of the cavum conchæ is bare. The annular cartilage is a complete ring. The osseous external auditory meatus is wide and extremely short.

The auricular muscles are thin. The scutularis is extensive and is divisible into interscutularis and fronto-scutularis. It partly covers the occipitalis muscle, which is oval and unpaired and ends in the fascia of the frontal region. The scutulo-auriculares superficiales, inferior et accessorius, and the cervico-scutularis are not differentiated as separate muscles. The cervico-auricularis superficialis and the parieto-auricularis both bifurcate and are inserted into the base of the concha and the scutiform cartilage. The parotido-auricularis is narrow and almost long enough to meet the opposite muscle. The tragicus consists of two parts; of these the lateral one is long and arises from the border of the mandible above the angular process. The helicis and the verticalis auriculæ are well developed.

The tympanic cavity is very roomy, extending ventrally into the large but simple cavity of the bulla ossea. The tympanic membrane is extensive and oval. The promontory is very pronounced. The auditory ossicles are large. The Eustachian tube is short, and has a fibrous outer wall. Its pharyngeal opening is an oblique slit situated on the lateral wall of the naso-pharyngeal meatus, and is margined internally by a thick mucous fold.

The cochlea has three and a half turns and is more sharply pointed than in the ungulates.

THE SKIN AND APPENDAGES

The skin varies greatly in thickness in different breeds. It is remarkably loose on the dorsal aspect of the neck and trunk, where it can be raised in extensive folds. The coat is also subject to extreme variation in length, thickness, color, etc. The hairs are arranged in groups of three to a large extent. The sebaceous glands are best developed in the short and rough haired breeds. They are largest and most numerous at the lips, anus, dorsal surface of the trunk, and sternal region. The sweat glands are relatively better developed in the long and fine haired breeds. The largest are found in the digital pads. Coil glands occur in the skin of the muzzle, the perineum, and the paranal pouches.

On the flexion surface of the carpus and digit there are hairless, cushion-like pads. The carpal pad (Torus carpalis) is situated medial and distal to the accessory carpal bone. The metacarpal and metatarsal pads (Torus metacarpalis, metatarsalis) are the largest and are situated behind the distal ends of the metacarpal or metatarsal bones and the greater part of the first phalanges. They are somewhat heart-shaped, with two unequal lateral lobes, and the apex distal. The metapodiophalangeal joints rest on them when the paw supports the weight. The digital pads (Tori digitales) are oval and are much smaller; they similarly support the second digital joints. That of the first digit is small on the fore limb, and usually absent from the hind limb. Each receives two suspensory bands from the tubercles at the distal end of the corresponding second phalanx. The pads have a basis of fibro-elastic tissue and fat, which is intimately adherent to the skin and is connected by trabeculæ with the bones and tendons. The epidermis is thick and largely keratinized, and is studded with numerous rounded papillæ which are readily seen with the naked eye. The corium has large papillæ, and contains sweat glands and lamellar corpuscles.

The =claws= (Ungues) correspond in form to the ungual part of the distal phalanges which they inclose. The horn of the claw consists of a body or wall and a sole. The former is strongly curved in both directions, and is compressed laterally. Its root or coronary border fits into the depression under the bony collar or ungual crest of the third phalanx and is covered by skin. The lateral borders converge and inclose the sole anteriorly. The matrix presents a coronary part which bears papillæ only near the coronary border. On the dorsal surface it is thickened to form a ridge, and the corresponding part of the horny covering is thick and maintains the pointed character of the claw. The matrix of the sides of the wall bears small laminæ which converge to the matrix of the sole. The latter is papillated. When the flexor muscles are inactive, the distal phalanges and the claws are maintained in dorsal flexion by two elastic ligaments. These arise from the tubercles at the proximal end of the second phalanx and converge to the dorsal aspect of the ungual crest of the third phalanx.

OLFACTORY AND GUSTATORY ORGANS

The =olfactory region= lies above the lamina transversa, which separates it from the naso-pharyngeal meatus. The mucous membrane is distinguished by its thickness and yellow color, and is very extensive. It covers about half of the large ethmoturbinals, and one-third to one-half of the septum nasi. The ethmoturbinal which projects into the frontal sinus and the adjacent inner wall of the sinus is olfactory in character. Olfactory nerve-fibers ramify in the vomero-nasal organ (of Jacobson).

The gustatory apparatus presents no special features of importance.

INDEX

Abdomen, muscles of, 245 of dog, 326 of pig, 313 muscles of, 301, 313

Abdominal aorta, 536 branches of, 566 of dog, 638 artery, anterior, 541 posterior, 579 subcutaneous, 580 cavity of horse, 352 of ox, 390 fascia of horse, 245 muscles of dog, 326 of horse, 245 of pig, 301, 313 panniculus, 245 plexuses, 713 tunic of horse, 245 of pig, 313 veins, 598

Abducent nerve, 683

Abduction of joints, 172

Abductor cruris posterior muscle, 327 digiti quinti muscle, 324, 329 hallucis muscle, 329 pollicis brevis et opponens pollicis muscle, 324

Abomasum of ox, 390, 392 cavity of, 396 of sheep, 409

Accelerator urinæ, 499

Accessory carpal bone, 84 fibro-cartilage of patella, 105 organs, 330 pancreatic duct of dog, 431 of horse, 373 pillars of rumen, 393 spleens of horse, 379 thyroids of dog, 468 of horse, 458 of ox, 464

Acetabular angle, 94, 96 fossa, 96 notch, 96

Acetabulum of dog, 167 of horse, 96 of ox, 131 of pig, 148

Acromion of dog, 162 of ox, 127

Adduction of joints, 172

Adductor brevis muscle of horse, 282 digiti quinti muscle of dog, 324 secunda muscle of dog, 324 hallucis muscle of dog, 329 longus muscle of horse, 282 magnus muscle of horse, 282

Adductor muscle of dog, 328 of horse, 282 of ox, 308 of pig, 316 parvus muscle of horse, 282 pollicis muscle of dog, 324

Aditus laryngis of horse, 447

Adrenal bodies of dog, 484 of horse, 477 structure of, 478 of ox, 481 of sheep, 481 plexus, 714

Adventitia of seminal vesicles, 492 of vas deferens, 489

Æquator lentis, 746

Æsthesiology, 734

Air-cells of lungs, 457

Alæ nasi, 436

Alar canal, 51 cartilage, 437 of ox, 459 fold, 437 foramen, 68

Alimentary canal, 330

Alveolar arch, superior, 69 artery, inferior, 552 of dog, 635 of pig, 627 border of mandible, 64 ducts of lungs, 457 nerve of dog, 729 of horse, 681, 682 periosteum of teeth, 339 tuberosity of horse, 69 vein, 589 inferior, 587

Alveoli of horse, 58 of lungs of horse, 457 of thyroid gland of horse, 458

Alveus, 669

Amphiarthroses, 172

Ampulla ductus deferentis, 489 of semicircular canals, 758 of uterus of bitch, 523 recti of horse, 370

Amygdaloid nucleus, 676

Anal glands of dog, 432 lymph glands, 605 of ox, 626 of pig, 632 sacs of dog, 432

Anastomosis of arteries, 524

Anatomy, 17 gross, 17 macroscopic, 17 microscopic, 17 philosophical, 17 special, 17

Anatomy, systematic, 17, 18 topographic, 17, 18 veterinary, 17

Anconeus muscle, 262 of pig, 315

Angiology, 524

Angle, duodenal, of horse, 372 of mandible, 64 splenic, 372

Angular artery of eye, 550 of ox, 611 movements of joints, 171 process of mandible of dog, 159

Annular cartilage of ear, 748 ligament, 212 anterior, of horse, 263 of manus of horse, 263 of pelvic limb of horse, 274 posterior, of carpus of horse, 263

Annulus tympanicus, 753

Ansate fissure of dog, 726

Anterior angle of pancreas, 372 of scapula, 76 annular ligament of horse, 263 aorta, 537 aperture of thoracic cavity, 450 fossa of skull, 70 nares, 436

Antero-external angle of ischium, 95

Antero-internal angle of ischium, 95

Antibrachial artery of dog, 635

Anticlinal vertebræ of horse, 42

Antitragicus muscle, 751

Antitragus, 748

Antrum pylori, 358

Anus of horse, 371 of ox, 400

Aorta, 535 abdominal, 536 branches of, 566 of dog, 638 anterior, 537 arch of, 535 of ox, 609 of pig, 627 thoracic, 536 branches of, 565

Aortic orifice of heart of horse, 533 plexus, 712

Aperture, anterior, of thoracic cavity, 450 of abdominal cavity, 353 pharyngeal, of horse, 447

Apex cæci, 364

Apical lobe of lungs of ox, 462, 463

Aponeuroses, 211

Aponeurosis of external oblique muscle, 246 of internal oblique muscle, 248 of transversus abdominis muscle, 249 pharyngeal, 350

Appendages of skin, 762

Appendix testis, 485 ventriculi laryngis, 447

Aquæductus cochleæ, 759 vestibuli, 758

Aqueduct of cerebrum, 664 of Sylvius, 664

Aqueous humor, 746

Arachnoid granulations, 647

Arachnoidea, 646 spinal, 647

Arch, alveolar, superior, of horse, 69 of aorta, 535 of cricoid cartilage, 441 plantar, 581 venous, 595 zygomatic, 56, 67

Arciform ligaments, 182

Arcuate fibers, external, 657, 658 internal, 658 of cerebellum, 661

Arcus terminalis, 564 venosus plantaris, 599 volaris, 595

Area acustica, 662 of ox, 715 centralis retinæ, 746 cochlæ, 759 parolfactoria, 671 radicularis ventralis, 649 tentorial, 668 vestibularis superior, 759

Arm, bones of, 28 muscles of, 259 of ox, muscles of, 302 of pig, muscles of, 314

Arrectores pilorum, 763

Arterial circle of Willis, 546 plantaris lateralis of ox, 620 reticularis of ox, 615

Arteries or artery, 534, 535 abdominal, anterior, 541 posterior, 579 alveolar, 552 of dog, 635 of pig, 627 anastomosis of, 524 angular, of eye, 550 of ox, 611 antibrachial, of dog, 635 asternal, 541 auricular, 550 of dog, 635 of ox, 611 of pig, 627 posterior, 550 axillary, 556 basilar, 546 bicipital, of dog, 635 brachial, 538, 556 deep, 559 of dog, 633, 635 of ox, 609, 612 of pig, 627 brachiocephalic, 538 of dog, 633 of pig, 627 bronchial, 457, 565 of ox, 614 of pig, 627 broncho-œsophageal, 565 buccinator, 555 of pig, 627 cæcal, 570 carotid, common, 541 of dog, 634 right, 542 external, 547 of ox, 611 internal, 546 of dog, 633, 634 of ox, 610 of pig, 627 central, of retina, 554 cephalic, 541 cerebral, 546 posterior, 546 cerebrospinal, 545 of dog, 634 cervical, deep, 540 inferior, 541 of dog, 633 of ox, 609 of pig, 627 superior, 540 ciliary, 554 circumflex, anterior, 558 external, 577 of ox, 619 of dog, 635 of ox, 612 of scapula, 556 posterior, 556 coccygeal, lateral, 577 middle, 575 of dog, 641 of ox, 618 cœliac, 566 of dog, 638 of ox, 614 of pig, 627 colic, 570 communicating posterior, 546 condyloid, 545 of dog, 634 of ox, 611 coronary, 535, 537 of dog, 632 of ox, 609 cremasteric, 578 dental, 552 inferior, 555 digital, 564 common, 563 of ox, 621 external, of ox, 614, 620 of dog, 637, 641 of pig, 629, 630 dorsal, 538 of dog, 633 of ox, 609 dorso-intercostal, 538 end, 524 ethmoid, 554 external coat, 525 facial, 547 of dog, 635 transverse, 550 femoral, 579 anterior, 580 deep, 580 of dog, 639 of ox, 619 of pig, 630 posterior, 580 femoro-popliteal, 580 frontal, 553 gastric, 506 of dog, 638 gastro-duodenal, 569 gastro-epiploic, 569, 570 gastro-hepatic, of pig, 627 gastro-splenic, of dog, 638 gluteal, anterior, 577 of dog, 641 of ox, 619 posterior, 575 hæmorrhoidal, 594 of dog, 641 hepatic, 377, 567 of dog, 638 of ox, 614 hypogastric, 573 ideal, 570 ileo-cæcal, 570 ileo-cæco-colic, of ox, 617 iliac, circumflex, 578 of dog, 639 external, 578 of ox, 619 internal, 573 of ox, 618 iliaco-femoral, 577 of ox, 619 ilio-lumbar, 577 of dog, 641 of ox, 619 of pig, 630 incisor, 552 infraorbital, 555 of dog, 635 of pig, 627 intercostal, 565 of ox, 614 of pig, 627 internal coat of, 525 interosseous, common, 561 dorsal, 562 of dog, 635 of ox, 612 recurrent, 561 intestinal, 570 intima of, 525 ischiatic, 575 of ox, 619 labial, 549 of ox, 611 superior, 550 lacrimal, 553 laryngeal, of ox, 610 lingual, 548 of dog, 634 of ox, 611 lumbar, 571, 573 of ox, 618 of pig, 629 malar, 555 mammary, 580 of ox, 619 masseteric, inferior, 547 of ox, 612 mastoid, 545 maxillary, external, 547 internal, 551 of ox, 612 of dog, 635 of ox, 611 of pig, 627 maxillo-muscular, 547 median, 559 of ox, 612 meningeal, anterior, 546 middle, 552 of dog, 634 posterior, 545 mental, 552 mesenteric, great, 570 of dog, 638 of ox, 615 of pig, 628, 629 posterior, of ox, 618 small, 571 metacarpal, dorsal, 562 external volar, 562 internal volar, 562 large, 563 of dog, 635, 636, 637 of ox, 614 of pig, 629 palmar, 563 metatarsal, 581 dorsal, 585 of ox, 620 great, 585 internal superficial plantar, 619 of dog, 640, 641 of pig, 630 middle coat of, 525 nasal, 550 of ox, 611 nutrient, of femur, 580 of humerus, 559 of tibia, 581 obturator, 577 of ox, 619 occipital, 544 of dog, 634 of ox, 611 of pig, 627 œsophageal, 565, 567 of ox, 614 of pig, 627 of adrenal bodies of horse, 478 of articulations, 171 of bladder of horse, 477 of bulb, 575 of clitoris, 575 of conjunctiva, 737 of corpus callosum, 546 of dog, 633 of external ear, 752 of eyelids, 737 of Fallopian tubes of mare, 511 of first phalanx, 564 of hoof, 771 of internal ear, 761 of ox, 609 of pelvic limb of ox, 619 of penis, 496 dorsal, 580 of pig, 627 of plantar cushion, 564 of rete carpi volare, 562 of retina, 746 of second phalanx, 564 of skin, 762 of small intestine, 570 of third phalanx, 564 of tympanum, 755 of uterus, 513 of vagina, 514 of vascular tunic of eye, 744 omaso-abomasal, of ox, 615 ophthalmic, 553 of dog, 635 of ox, 612 orbital, 555 ovarian, 571 of mare, 510 palatine, 555 of pig, 627 palato-labial, 555 pancreatic, 569 pancreatico-duodenal, 569 parotid, 543 of pig, 627 perineal, 574 of dog, 641 peroneal, 585 perpendicular, 564 pharyngeal, 548 of ox, 611 phrenic, 565 of ox, 614 phrenico-abdominal, of dog, 639 of pig, 628 plantar, 581 of dog, 640 of ox, 619 popliteal, 581 of ox, 619 of pig, 630 preplantar, 564 prepubic, 579 prevertebral, 545 pterygoid, 552 pudic, external, 580 internal, 573 of pig, 630 pulmonary, 457, 524, 535 pyloric, 569 radial, anterior, 559 of dog, 635 of ox, 613 posterior, 559 of ox, 612 renal, 475, 571 of dog, 639 of ox, 618 of pig, 628 reticular, of ox, 615 ruminal, of ox, 615 sacral, lateral, 575 middle, of ox, 618 of ox, 619 saphenous, 580 of dog, 640 of ox, 619 of pig, 630 sheath of, 525 spermatic, 487, 489, 571 of dog, 639 of ox, 618 of pig, 627 sphenopalatine, 555 splenic, 569 of dog, 658 of ox, 615 of pig, 628 staphyline, 555 structure of, 525 stylo-mastoid, 550 subcostal, 539 of dog, 633 of ox, 609 sublingual, 548 of dog, 635 submaxillary, 547 submental, 549 subscapular, 556 of dog, 635 of ox, 612 supraorbital, 553 suprascapular, 556 systemic, 524 tarsal, external, 581 of pig, 630 perforating, 585 temporal, anterior deep, 553 of dog, 635 of ox, 612 posterior, deep, 552 superficial, 550 terminal, 524 thoracic, external, 541 internal, 540 of dog, 633 of ox, 609 of pig, 627 thoracico-dorsal, 556 thyroid, accessory, 543 of ox, 610 of pig, 627 thyro-laryngeal, 543 tibial, anterior, 583 of dog, 641 of ox, 620 of pig, 630 posterior, 581 recurrent, 581 tympanic, 552 ulnar, 559 of dog, 637 of ox, 613 superior collateral, of ox, 612 umbilical, 574, 606 of ox, 619 uterine, 571 middle, 578 of dog, 641 of ox, 619 posterior, 574 utero-ovarian, 571 of dog, 639 of ox, 618 vertebral, 540 of dog, 633 of ox, 609 vesical, 574 vesico-prostatic, 574 volar, deep, 562 of second phalanx, 564

Arthrodia, 172

Arthrology, 169 comparative, 203

Articular cartilage, 170 discs, 171

Articularis genu muscle of ox, 307

Articulatio carpi of horse, 183

Articulations, 169, 172 abduction of, 172 adduction of, 172 angular movements, 171 arteries of, 171 atlanto-axial, 176 atlanto-occipital, 176 basi-cornual, 180 capsule, 170 carpal, 183 of dog, 205 of ox, 205 of pig, 205 carpo-metacarpal, 183 cavity of, 170 chondro-sternal, 178 circumduction of, 171 classification of, 169 coccygeal, 175 coffin, 189 costo-central, 177 costo-chondral, 178 costo-transverse, 177 costo-vertebral, 177 crico-arytenoid, 444 crico-thyroid, 444 dorsal flexion of, 171 elbow, 181 of dog, 205 of ox, 205 of pig, 205 extension of, 171 femoro-patellar, 194 femoro-tibial, 196 fetlock, 185 flexion of, 171 folds of, 170 gliding movements of, 171 hip, 192 of dog, 209 of ox, 209 of pig, 209 hock, 199 of dog, 210 of ox, 210 of pig, 210 hyoidean, 180 intercarpal, 183 intercentral, 173 intercornual, 180 intermetacarpal, of dog, 206 of ox, 206 of pig, 206 interneural, 173 interphalangeal, distal, 189 of dog, 209 of ox, 208 of pig, 208 proximal, 188 intertransverse, 175 knee, 183 metacarpo-phalangeal, 185 of dog, 208 of ox, 206 of pig, 208 movable, 170 movements of, 171

Articulations, nerves of, 171 of larynx, 444 of pelvic limb, 190 of dog, 209 of ox, 209 of pig, 209 of ribs, 177 of skull, 179 of thoracic limb, 180 of dog, 205 of ox, 205 of pig, 205 of thorax, 177 of dog, 204 of ox, 204 of pig, 204 overextended, 171 pastern, 188 plantar flexion of, 171 radio-carpal, 183 radio-ulnar, 182 rotation of, 172 sacral, 175 sacro-iliac, 190 of dog, 209 of ox, 209 of pig, 209 shoulder, 180 of dog, 205 of ox, 205 of pig, 205 sternal, 178 stifle, 194 of dog, 209 of ox, 209 of pig, 209 surfaces of, 170 synovial layer of, 170 temporo-hyoid, 180 temporo-mandibular, 179 of dog, 204 of ox, 204 of pig, 204 thyro-hyoid, 444 tibio-fibular, 199 of dog, 210 of ox, 209 of pig, 210 tibio-tarsal, 199 true, 170 veins of, 171 vertebral column, 172 of dog, 204 of ox, 203 of pig, 204 villi of, 170 volar flexion of, 171

Arytenoid cartilages of larynx, 443 of dog, 467 of ox, 459 of pig, 465 ligament, transverse, of larynx, 444

Arytenoideus transversus muscle of larynx of horse, 446

Asternal artery, 541 ribs, 25 of horse, 43

Astragalo-calcaneal ligaments, 202

Astragalo-scaphoid ligaments, 202

Atlantal gland of ox, 623

Atlanto-axial articulation of horse, 176 ligament, inferior, 176 superior, 176

Atlanto-occipital articulation, 176 membrane, inferior, 176 superior, 176

Atlas, 33, 34 of dog, 150 of ox, 112 of pig, 147

Atrio-ventricular groove of heart, 527 opening in left atrium, 530 in right atrium, 530 left, of ventricle, 533 right, of ventricle, 531

Atrium of heart, 529 left, 530 right, 529 openings in, 529 sinus of, 529 ventriculi of ox, 393

Auditory canal, external, 747, 748 meatus, external, 56, 748 internal, 56, 759 nerve, 686 ossicles, 754 process, external, 56, 67 tube, 755

Auricle of horse, 747

Auricular artery, anterior, 550 of dog, 635 of pig, 627 posterior, 550 of ox, 611 branch of vagus, 687 cartilage, 748 lymph gland of dog, 643 muscles, 749 of dog, 780 of ox, 774 nerve, 685 posterior, 695 vein, 588

Auriculopalpebral nerve, 685 of dog, 729 of ox, 717

Axillary artery, 556 ligament of Helmholtz, 755 lymph glands, 605 of dog, 643 of ox, 625 of pig, 631 nerve of horse, 697

Axis, 34 development of, 35 lentis, 747 of dog, 150 of ox, 112 of pelvis, 97 of ox, 133 of pig, 137 optic, 740

Azygos uvulæ, muscle of, 333

Back, fasciæ of, 235 superficial, 235 muscles of, 235 of dog, muscles of, 325 of ox, muscles of, 300

Back of pig, muscles of, 313

Ball-and-socket joint, 172

Bands, longitudinal, of cæcum, 364 muscular, of great colon, 368

Bars of hoof, 764

Bartholin’s ducts of mare, 515 glands of cow, 519

Basi-cornual articulation, 180

Basihyoid bone, 64

Basilar artery, 546 plexus, 592 venous, 592 process, 48 of third phalanx, 91

Basis pedunculi, 664

Belly of muscle, 212

Biceps brachii, 259 of dog, 322 of pig, 314 femoris muscle, 278 of dog, 326 of ox, 306 of pig, 316 rotator tibialis, 280 of ox, 302

Bicipital artery of dog, 635 bursa of horse, 259 groove of humerus, 79 tuberosity of radius, 81 of scapula, 77

Bicuspid valve, 533

Bifurcation of trachea, 449

Bile-duct, common, of sheep, 410 of dog, 431 of ox, 398 of pig, 419, 422

Bipennate muscle, 212

Biventer cervicis muscle of dog, 325

Bladder, 469, 475 arteries of, 477 blood-supply of, 477 fixation of, 476 lateral ligaments of, 476 lymph vessels of, 477 middle ligament of, 476 mucous coat of, 476 muscular coat of, 476 neck of, 416 nerves of, 477 of dog, 484 of ox, 480 of pig, 483 relations of, 476 round ligament of, 476 serous coat of, 476 sphincter of, 476 structure of, 476 trigonum of, 476 veins of, 477 vertex of, 476

Blind sacs of rumen of ox, 392

Blood-vascular system, 524, 525 of dog, 632 of ox, 608

Blood-vessels, 524 of cornea, 742

Body, ciliary, 743 geniculate, 665 of dog, 725 of ox, 716

Body, mammillary, 665 of dog, 726 pineal, 665 of ox, 716 pituitary, 664, 665 of dog, 726 of ox, 716 restiform, 656 vitreous, 746 of ox, 774

Bone or bones, acetabulum, of pig, 148 acromion, of dog, 162 air-spaces, 21 arteries, 21 atlas, 33 of dog, 150 of ox, 112 of pig, 137 axis, 34 of dog, 150 of ox, 112 of pig, 137 basihyoid, 64 carpal, 28, 83 of dog, 164 of ox, 129 of pig, 147 cartilage, 22 cavities, 23 chemical composition, 23 chevron, of dog, 152 clavicle, 27 of dog, 162 compact substance, 20 coracoid, 27 cranial, 27, 47 of dog, 154 of ox, 115 of pig, 139 depressions, 23 descriptive terms, 23 development and growth, 22 digital, 28, 30 diploë, 21 eminences, 23 ethmoid, 52 of dog, 157 of ox, 116 of pig, 142 facial, 27, 57 of dog, 157 of ox, 120 of pig, 142 femur, 29, 97 of dog, 167 of ox, 133 of pig, 148 fibula, 29, 104 of dog, 168 of ox, 134 of pig, 149 flat, 19 frontal, 55 of dog, 155 of ox, 118 of pig, 141 hock, 105 of ox, 134 of pig, 149 humerus, 28, 77 of dog, 162 of ox, 127 of pig, 146

Bone, hyoid, 64 of dog, 159 of ox, 122 of pig, 144 ilium, 29, 93 of dog, 165 of ox, 131 of pig, 148 interparietal, 53 of dog, 155 of ox, 116 of pig, 140 irregular, 19 ischium, 29, 95 of dog, 165 of ox, 131 of pig, 148 lacrimal, 61 of dog, 158 of ox, 121 of pig, 143 long, 19 lymph vessels, 21 malar, 62 of dog, 158 of ox, 121 of pig, 143 mandible, 63 of dog, 158 of ox, 122 of pig, 143 marrow, 21 maxilla, 58 of dog, 157 of ox, 120 of pig, 142 medullary arteries, 21 cavity, 20 membrane, 22 metacarpal, 28, 87 of dog, 164 of ox, 130 of pig, 147 metatarsal, 30, 110 of dog, 168 of ox, 135 of pig, 149 nasal, 61 of dog, 158 of ox, 121 of pig, 143 navicular, 92, 111 nerves, 21 number, 19 occipital, 47 of dog, 154 of ox, 115 of pig, 139 of arm, 28 of face, 27 of forearm, 28 of forefoot, 28 of hand, 28 of leg, 29 of pelvic limb, 29, 92 of dog, 165 of ox, 131 of pig, 148 of skull, 27, 47 of dog, 153 of ox, 115 of pig, 139 of thoracic limb, 27, 74 of dog, 162

Bones, of thoracic limb of ox, 127 of pig, 146 of thorax, 27, 47 of dog, 153 of ox, 115 of pig, 139 os coxæ, 29, 92 of pig, 14 palatine, 60 of ox, 120 of pig, 142 parietal, 54 of dog, 155 of ox, 117 of pig, 140 patella, 29, 104 of dog, 168 of ox, 134 of pig, 149 pelvic, 96 of dog, 167 of ox, 132 of pig, 148 perforations, 23 periosteal arteries, 21 periosteum, 21 phacoid, of cat, 164 phalanges, 29, 89, 111 of dog, 165 of ox, 130, 136 of pig, 148, 150 physical properties, 23 premaxilla, 59 of dog, 157 of ox, 120 of pig, 142 prenasal, of pig, 143 prominences, 23 pterygoid, 60 of dog, 158 of ox, 121 of pig, 143 pubic, 29, 95 of dog, 167 of ox, 131 of pig, 148 radius, 28, 80 of dog, 163 of ox, 127 of pig, 147 red marrow, 21 ribs, 25, 43 of dog, 153 of ox, 114 of pig, 138 rostri, of pig, 143 sacrum, 39 of dog, 151 of ox, 114 of pig, 138 scapula, 27, 74 of dog, 162 of ox, 127 of pig, 14 sesamoid, 29, 92, 111 developing in tendon tissue, 211 distal, 29 of dog, 165 of ox, 131, 136 of pig, 148 proximal, 29 short, 19

Bone, sinuses, 21 sphenoid, 50 of dog, 156 of ox, 115 of pig, 141 spongy substance, 20, 21 sternum, 26, 45 of dog, 153 of ox, 115 of pig, 139 structure of, 20 tarsal, 29, 105 of dog, 168 of ox, 134 of pig, 149 temporal, 55 of dog, 156 of ox, 120 of pig, 141 thigh, 29 thorax, 47 of dog, 153 of ox, 115 of pig, 139 tibia, 29, 100 of dog, 167 of ox, 134 of pig, 149 tibial, 29 tissue, 20 tubula vitrea, 21 turbinal, 62, 438 of dog, 158 of ox, 122 of pig, 143, 465 ulna, 28, 82 of dog, 163 of ox, 128 of pig, 147 veins, 21 vertebræ, 24, 31 anticlinal, 42 caudal, 24 cervical, 24 coccygeal, 24, 41 diaphragmatic, 42 lumbar, 24, 38 of dog, 150 of ox, 112 of pig, 136 sacral, 24 thoracic, 24, 35 vessels, 21 vomer, 63 of dog, 158 of ox, 122 of pig, 143 yellow marrow, 21 zygomatic, of horse, 62

Brachia conjunctiva, 661

Brachial artery, 538, 556 deep, 559 of dog, 633, 635 of ox, 609, 612 of pig, 627 plexus, 696 of dog, 730 of ox, 717 of pig, 723 triceps, 260 vein, 593 of dog, 642

Brachialis anticus, 260 muscle, 260

Brachialis muscle of dog, 322 of pig, 315

Brachiocephalic artery, 538 of dog, 633 of pig, 627 trunk of aorta, 537 veins of dog, 641

Brachio-radialis muscle of dog, 322

Brachium pontis, 659

Brachycephalic breed of dogs, 159

Brain, development of, 655 of dog, 724 of horse, 652 of ox, 715 of pig, 720 veins of, 592

Bristles of pig, 778

Broad ligaments of uterus, 356 of bitch, 523 of cow, 518 of mare, 513

Broca’s parolfactory area, 671

Bronchi, interlobular, 457 of dog, 468 of horse, 450, 456 structure of, 456 of ox, 460 of pig, 466

Bronchial artery, 457, 565 of ox, 614 of pig, 627 branches of lungs, 456 of vagus, 690 lymph glands, 457, 603 of dog, 643 of pig, 631 vein, 587

Bronchioles, lobular, 457 respiratory, 457

Broncho-œsophageal artery, 565

Brush of ox, 775

Buccal fascia, 213 glands, 332 of ox, 383 of pig, 410 nerve, 685 of dog, 729 of ox, 717 of pig, 722

Buccinator artery, 555 of pig, 627 muscle, 216 of dog, 318 of ox, 295 nerve of horse, 681 vein, 590 of pig, 630

Bulb of hair, 763 olfactory, 671 of dog, 727 of ox, 717 of pig, 721

Bulbar conjunctiva, 736 fascia of horse, 738

Bulbi vestibuli of mare, 515 olfactorius, 671

Bulbo-cavernosus muscle of penis of ox, 503 of urethra of horse, 499

Bulbo-urethral glands of dog, 506

Bulbo-urethral glands of horse, 493 structure of, 494 of ox, 503 of pig, 505

Bulbus aortæ, 536 oculi, 739

Bulla, lacrimal, of ox, 121 ossea, 57

Burdach’s column, 652

Bursa, bicipital, 259 navicular, of deep digital flexor muscle, 272 of biceps femoris muscle, 279, 280 of flexor pedis perforatus muscle, 293 of gastrocnemius muscle, 290 of rectus femoris muscle, 284 of semitendinosus muscle, 280 ovarica of mare, 511 ovarii of bitch, 522 podotrochlearis, 272 supra-atloid, 174 supraspinous, of horse, 175 of anterior digital extensor muscle, 265 synovial, of infraspinatus muscle, 256 of lateral digital extensor muscle, 266 of teres minor muscle, 257

Bursal synovial membrane, 211

Cæcal artery, 570 lymph glands of pig, 632

Cæco-colic fold, 367 orifice, 364

Cæcum, 363 of dog, 431 of ox, 398 of pig, 420 of sheep, 409 cupulare, 760 vestibulare, 760

Calcaneo-cuboid ligaments, 202

Calcaneo-cunean ligaments, 202

Calcaneo-metatarsal ligament, 201

Calcaneo-scaphoid ligament, 202

Caliber of great colon of horse, 367

Callosal sulcus, 669

Callosomarginal fissure, 669 of dog, 727 of ox, 716 of pig, 721

Calyces majores, 480 minores, 480

Camera oculi, 746

Canal, alar, 51 auditory, external, 748 carotid, 156 carpal, 86 cervical, of cow, 518 of mare, 512 condyloid, of ox, 115 dental, inferior, of horse, 64

Canal, dental, superior, of horse, 59 facial, of horse, 56 femoral, of horse, 282 for naso-lacrimal duct of horse, 71 infraorbital, of horse, 59 inguinal, of horse, 249 lacrimal, osseous, of horse, 61 mandibular, of horse, 64 medullary, of metacarpus of ox, 130 naso-palatine, of ox, 384 of Gartner, 519 of tarsus of horse, 109 of temporal bone of dog, 156 palatine, of horse, 58 parieto-temporal, of horse, 54, 57 petro-basilar, of dog, 156 pterygoid, of horse, 51, 61 sacral, of horse, 41 semicircular, membranous, 760 osseous, 758 semilunar, 91 spiral, of cochlea, 759 subsphenoidal, of horse, 51 supraorbital, of ox, 119 vertebral, of horse, 42 Vidian, of horse, 51, 61

Canalis centralis, 650

Canine teeth, 338, 341, 346 of dog, 425 of ox, 386 of pig, 412

Canthi of eye, 735

Capillaries, 524

Capped hock, 293

Capsular ligament, 170

Capsularis muscle of dog, 328 of horse, 258, 286 of ox, 307 of pig, 314, 317

Capsule, external, 675 fibrous, of liver, 376 internal, 676 joint, 170 of horse, 174 of articulation, 176 of carpal joints, 183 of coffin joint, 189 of elbow joint, 181 of femoro-patellar articulation, 194 of femoro-tibial articulation, 197 of fetlock joint, 185 of hip joint, 192 of hock joint, 200 of lens, 747 of pastern joint, 188 of sacro-iliac articulation, 190 of shoulder joint, 180 of temporo-mandibular articulation, 179 of tenon, 738 of tibio-fibular articulation, 199 splenic, 379

Caput laterale tricipitis, 261

Caput longum tricipitis, 261 mediale tricipitis, 261

Cardiac bronchus of vagus, 690 glands of stomach of horse, 360 impression of lungs of horse, 454 lobe of lungs of ox, 463 muscle, 211 nerves, 712 notch of lungs of horse, 456 plexus, 712 sphincter of horse, 359 veins, 586

Cariniform cartilage, 46

Carnassial teeth of dog, 426

Carotid artery, common, 541 left, 543 of dog, 634 of ox, 610 right, 542 external, 547 internal, 546 of dog, 633, 634 of ox, 611 of pig, 627 canal of dog, 156 foramen of dog, 156 notch of horse, 51 plexus, 711

Carpal articular surface of radius of horse, 82 bones, 28 accessory, 84 canal of horse, 86 fascia of horse, 263 glands, 778 groove of horse, 86 joints of dog, 205 of horse, 183 of ox, 205 of pig, 205 pads of dog, 780 sheath of deep digital flexor muscle, 272 of superficial digital flexor muscle, 271

Carpo-metacarpal joint of horse, 183 sac of horse, 183

Carpus, 28 of dog, 164 of horse, 83 development of, 86 of ox, 129 of pig, 147

Cartilage, or cartilages, alar, of horse, 437 of ox, 459 annular, of cow, 748 articular, 170 arytenoid, of larynx, 443 of dog, 467 of ox, 459 of pig, 465 auricular, 748 bones, 22 cariniform, 46 conchal, 748 costal, 25, 26 of horse, 45 cricoid, of dog, 467 of horse, 441

Cartilage, cricoid, of ox, 459 of pig, 465 ensiform, of horse, 46 epiglottic, of dog, 467 of horse, 442 of ox, 459 of pig, 465 epiphyseal, 22 interarytenoid, of dog, 467 of pig, 465 lateral, of third phalanx of horse, 91 marginal, 171 of larynx of horse, 441 of nasal septum of horse, 437 of nostrils of ox, 459 parietal, of nasal cavity of horse, 437 scapular, of horse, 75 scutiform, 748 semilunar, of horse, 196 thyroid, of dog, 467 of horse, 442 of ox, 459 of pig, 465 xiphoid, 26 of horse, 46

Cartilagines tracheales of horse, 450

Caruncle, lacrimal, 735

Caruncula lacrimalis, 735 of dog, 779 of pig, 778 sublingualis of horse, 334

Cauda equina of horse, 648

Caudate ligament of horse, 375 lobe of liver, 433 of ox, 402 of pig, 421 nucleus, 675

Cavernous plexus, 711 sinus, 542

Cavity, abdominal, of ox, 390 cranial, of dog, 161 of horse, 69 of ox, 124 of pig, 145 glenoid, of horse, 67, 68, 76 joint, 170 nasal, of dog, 161, 466, 467 of horse, 71, 436 of ox, 125, 458 of pig, 145, 464 of abomasum of ox, 396 of larynx of horse, 447 of mouth of horse, 330 of omasum of ox, 395 of rumen of ox, 393 of tunica vaginalis of horse, 490 of uterus of mare, 513 pelvic, of horse, 97 of ox, 133, 390 sigmoid, of ulna of horse, 82 thoracic, of horse, 450 of ox, 461

Cavum conchæ of dog, 780 epidurale, 646 subdurale, 646 tympani, 752 of dog, 780 of ox, 775

Cavum tympani of pig, 778

Cells, air, of lungs of horse, 457 ethmoidal, of horse, 52 gustatory, 772

Cement of teeth, 339

Center, tendinous, of diaphragm of horse, 243

Central artery of retina, 554 canal of cord, 650 tarsal bone of horse, 107 of ox, 134

Cephalic artery, 541 index of dog, 159 part of sympathetic system, 711 vein, 591, 593 of dog, 642 of ox, 622

Cerebellar peduncles, 661 middle, 659 tract, direct, 661 veins, 592

Cerebello-olivary fasciculus, 658

Cerebellospinal fasciculus, 661

Cerebellum of dog, 725 of horse, 660 of ox, 716 of pig, 720

Cerebral arteries, 546 posterior, 546 fissures of horse, 668 of ox, 716 gyri of horse, 668 hemispheres, 667 of dog, 726 of ox, 716 of pig, 721 nerves of horse, 676 peduncles, 664 of ox, 716 of pig, 720 vein, 588, 592 of ox, 621

Cerebro-spinal artery, 545 of dog, 634 fasciculi, 660

Ceruminous glands, 749

Cervical artery, deep, 540 inferior, 541 of dog, 633 of ox, 609 of pig, 627 superior, 540 branch of facial nerve, 685 canal of cow, 518 of mare, 513 enlargement of horse, 648 ganglia, 711 of dog, 733 of ox, 720 of pig, 724 lymph glands, 601 of dog, 643 of pig, 631 nerves of horse, 694 part of sympathetic nervous system, 711 plexus, 694 vein, deep, 586 inferior, 591 vertebræ, 24 of dog, 150 of horse, 32

Cervical vertebræ of ox, 112 of pig, 136

Cervicalis ascendens muscle, 225

Cervico-auricularis, 750 of dog, 780 of ox, 784

Cervico-scutularis, 749 of dog, 780 of ox, 774

Cervix uteri of cow, 517 of mare, 513 of sow, 522

Chambers of eye, 746

Check ligament, inferior, of carpal joints, 183 of deep digital flexor muscle, 272 of hock joint, 200 superior, of superficial digital flexor muscle, 270

Cheek teeth, 338, 342 deciduous, of horse, 346 of dog, 425 of ox, 386 of pig, 412 of sheep, 405

Cheeks of dog, 423 of horse, 332 muscles of, 213 of ox, 382 of pig, 410 of sheep, 405

Chestnut, 771

Chevron bones of dog, 152

Chiasma opticum, 666

Choanæ, posterior, of horse, 68

Chondro-pharyngeus muscle of horse, 350

Chondro-sternal articulations of horse, 178

Chorda tympani, 683, 684

Chordæ tendineæ, 531, 533

Chorioid, 742 fissure, 670 of dog, 779 of pig, 778 plexus of fourth ventricle, 657, 663 of lateral ventricle, 670, 675 of third ventricle, 666

Cilia, 735

Ciliary arteries, 554 body, 743 border of iris, 744 ganglion, 679, 711 of ox, 717 muscle, 743 nerve of dog, 728 of horse, 679 processes, 743 ring, 743

Circle, coronary, 564 of Willis, 546

Circulation, fœtal, 606 pulmonary, 607

Circulatory system of dog, 632 of ox, 608 of pig, 626

Circulus arteriosus major, 744

Circumanal glands of dog, 432

Circumduction of joints, 171

Circumflex artery, anterior, 558 external, 577 of ox, 619 of coronary cushion, 564 of dog, 635 of ox, 612 of scapula, 556 posterior, 556 iliac artery, 578 nerve of horse, 697 vein, external, 598

Cistern, milk, of cow, 521

Cisterna chyli, 600 of dog, 643

Cisternæ subarachnoidales, 646

Clarke’s column, 651

Claustrum, 675

Clavicle, 27 of dog, 162

Claws of dog, 781 of ox, 775 of pig, 779

Cleft, palatine, of horse, 60, 69, 71 vulvar, of mare, 514

Cleido-cervicalis muscle of dog, 320

Cleido-mastoideus muscle of dog, 320 of horse, 252 of pig, 314

Cleido-occipitalis muscle of pig, 314

Cleido-transversarius muscle of horse, 252

Clinoid process of sphenoid bone of dog, 156 of pig, 142

Clitoris, artery of, 575 of bitch, 523 of cow, glans of, 519 of mare, 515 prepuce of, 515 of sow, 522

Coccygeal artery, lateral, 577 middle, 575 of dog, 641 of ox, 618 fascia of horse, 238 ganglion, 713 nerves of horse, 710 vertebræ, 24 of dog, 152 of horse, 41 of ox, 114 of pig, 138

Coccygeus muscle of dog, 325 of horse, 238 ventralis lateralis muscle of horse, 240

Cochlea, 759 of dog, 780

Cochlear nerve, 686, 761

Cœliac artery, 566 of dog, 638 of ox, 614 of pig, 627 lymph gland of ox, 626 plexus, 714

Cœliaco-mesenteric ganglia, 714

Coffin bone of horse, 90 joint, 189

Coffin joint, capsule of, 189 lateral ligaments of, 189 movements of, 190

Colic arteries, 570 lymph glands of pig, 632 mesentery of horse, 354, 369

Collateral fissure of dog, 726 vessel, 524

Colliculus facialis, 662 seminalis of horse, 499 of ox, 504

Colon, great, of horse, 365 of dog, 432 of ox, 398 of pig, 420 of sheep, 409 small, of horse, 369 tæniæ of, 370

Column of Burdach, 652 of Goll, 652 of spinal cord, 651 renal, of horse, 473

Columna grisea of cord, 650

Columnæ fornicis, 673

Comma-shaped tract, 652

Commissura grisea, 650 hypothalamica, 665

Commissure, hippocampal, 670 of nostrils of horse, 436 of spinal cord, 650 of vulva of mare, 515 optic, 666

Common bile-duct of sheep, 410

Communicating artery, posterior, 546

Compact substance of bone, 20

Complexus muscle of dog, 325 of horse, 231 of pig, 312

Compressor coccygis muscle of horse, 238

Concha of pig, 778

Conchal cartilage, 748

Condyle, external, of humerus of horse, 80 internal, of humerus of horse, 79 occipital, of horse, 48, 68, 69 of femur of horse, 99 of mandible of horse, 64 of temporal bone of horse, 55 of tibia of horse, 101

Condyloid artery, 545 of dog, 634 of ox, 611 canal of ox, 115 fossa of horse, 48, 68 vein, 588

Conjugal ligament of horse, 177

Conjugate diameter of pelvis of horse, 97 of ox, 132

Conjunctiva, 736 of ox, 772

Conjunctival sac, 736

Constrictor vestibuli muscle of mare, 515 vulvæ of mare, 515

Conus arteriosus of horse, 530

Conus medullaris of horse, 648, 649 vasculosus of epididymis of horse, 487

Coraco-brachialis muscle of dog, 322 of horse, 258 of ox, 302 of pig, 314

Coracoid, 27 process of horse, 77

Coraco-radialis muscle of horse, 259

Cord, spinal, of dog, 724 of horse, 648 of ox, 715 of pig, 720

Cores, horn-, of ox, 118

Corium, 762 of dog, 780

Cornea of dog, 779 of horse, 741 of ox, 774 of pig, 778

Cornu ammonis, 669 anterior, of thyroid cartilage of horse, 442 of nostrils of horse, 437 posterior, of thyroid cartilage of horse, 442

Cornua, great, of horse, 65 middle, of horse, 65 small, of horse, 65 thyroid, of horse, 65 uteri of cow, 517 of mare, 511

Corona glandis of penis of horse, 495 radiata, 676

Coronal border of hoof, 765 fissure of dog, 726 of ox, 716 of pig, 721

Coronary arteries, 535, 537 of dog, 632 of ox, 609 circle, 564 groove of heart, 527 of hoof, 765 of rumen of ox, 392 ligament of horse, 374 matrix, 769 pillars of rumen of ox, 393 plexus, 595 sinus, 585 of horse, opening of, 529 veins, 535, 586

Coronoid fossa of humerus of horse, 80 process of mandible of horse, 64 of radius of horse, 80

Corpora quadrigemina, 663 of dog, 725

Corpus adiposum of eye, 738 albicans of mare, 510 callosum, 672 of ox, 716 cavernosum penis of horse, 495 fornicis, 673 geniculatum mediale, 665 luteum of mare, 510 Luysi, 665

Corpus medullare of cerebellum, 661 papillare, 762 rubrum of mare, 510 spongiosum of horse, 495 striatum, 675 trapezoideum, 655 of dog, 725 of ox, 715 of pig, 720 vitreum, 746

Corpuscles, Malpighian, of horse, 379, 473 renal, of horse, 473, 474

Corrugator supercilii muscle of horse, 218

Cortex of thymus gland of horse, 458

Corticopontile fibers, 660

Costal arch, 26 cartilages, 25, 26 of horse, 45 facets of thoracic vertebræ, 36, 37 groove, 26 pleura of horse, 451

Costo-central articulations of horse, 177

Costo-chondral articulations of horse, 178

Costo-sternal ligament, superior, of horse, 178

Costo-transverse articulations of horse, 177

Costo-vertebral articulations of horse, 177

Cotyledons, uterine, of cow, 518

Cotyloid ligament of horse, 192

Cowper’s glands of horse, 493, 506 of ox, 503 of pig, 505

Coxal angle of ilium of horse, 94

Cranial bones, 27 of dog, 154 of horse, 47 of ox, 115 of pig, 139 cavity of dog, 161 of horse, 69 of ox, 124 of pig, 145 nerves of dog, 728 of horse, 676 of ox, 717 of pig, 722 roots of, 656 superficial origins of, 653 region of horse, 67, 68 sutures of horse, 179

Cranio-facial index of dog, 159

Cremaster, external, of horse, 249, 490 of ox, 500 of pig, 313 of testicle of pig, 504

Cremasteric artery, 578

Crest, facial, of horse, 58, 62, 68 frontal, of horse, 55, 66 nasal, of horse, 71

Crest, occipital, of horse, 50, 69 of femur of horse, 99 of ilium of horse, 94 of sacrum of ox, 114 parietal, of ox, 117 petrosal of horse, 57, 70 pterygoid, of horse, 51 renal, of horse, 473 sagittal, of horse, 54, 66 semilunar, of third phalanx of horse, 91 spheno-occipital, of horse, 51 sublingual, of horse, 348 supracondyloid, of femur of horse, 97 tibial, of horse, 100 turbinal, inferior, of horse, 58 superior, of nasal bones of horse, 61 urethral, of male horse, 499 zygomatic, of horse, 58, 62

Cribriform plate of ethmoidf horse, 52

Crico-arytenoid joints of horse, 444

Crico-arytenoideus lateralis muscle of horse, 445, 446

Cricoid cartilage of dog, 467 of horse, 441 of ox, 459 of pig, 465

Crico-pharyngeus muscle of horse, 350

Crico-thyroid joints of horse, 444 membrane of horse, 444

Crico-thyroideus muscle of horse, 445

Crico-tracheal membrane of horse, 445

Crista galli of horse, 52, 70 terminales of horse, 530 vestibuli, 758

Cristæ acusticæ, 760 ungulæ, 765

Crown of tooth, 339

Crucial fissure of ox, 717 ligaments of femoro-tibial articulation of horse, 198

Cruciate fissure of dog, 727 of pig, 721

Crura cerebri, 664 fornicis, 673 helicis, 748 of dog, 779 of diaphragm of horse, 243

Crural fascia of horse, 274 nerve, anterior, of horse, 706 triceps muscle of horse, 284

Crureus muscle of horse, 286

Crystalline lens, 746

Cubital lymph glands, 606 of dog, 643

Cuboido-cunean ligaments of horse, 202

Cuboido-scaphoid ligament of horse, 202

Cuneate tubercle of pig, 720

Cuneiform cartilage of larynx of dog, 467

Cupola, 759

Curvator coccygis muscle of horse, 239

Cushion of hoof, 769 plantar, 771 Cutaneous glands of ox, 775 nerve of leg of horse, 708 of neck, 695

Cutaneus maximus muscle of abdomen, 245 scapulæ et humeri muscle, 255

Cuticular ridge of stomach, 360

Cystic duct of ox, 403

Dartos of scrotum of horse, 488

Deciduous canine teeth, 346 cheek teeth, 346 incisor teeth, 346 of ox, 386 teeth, 346

Decussatio lemniscorum, 658

Decussation of fillet, 658 of pyramids, 655 of superior peduncle of cerebellum, 661 pyramidal, 658

Deep abdominal fascia, 245 digital flexor muscle, 271 of dog, 323, 329 of leg, 293 of ox, 305 of pig, 316, 317 fascia, 212 of forearm, 262 of head of horse, 213 of neck of horse, 224 of shoulder of horse, 255 flexor muscle of ox, 311 gluteus muscle, 278 pectoral muscle, 253, 254 of dog, 320 of ox, 302 of pig, 314 sesamoidean ligament, 188

Deferential fold of testicles, 491

Deltoid muscle, 255 of dog, 320 of ox, 302 of pig, 314 tuberosity of horse, 78

Dental artery, 552 superior, 555 canal, inferior, 64 superior, 59 nerve, 681, 682 plate of ox, 384 vein, 587

Dentine, 339

Depressor coccygis muscle, 240 labii inferioris muscle, 216 of dog, 318 of ox, 295 of pig, 311 superioris muscle of ox, 295 nerve of dog, 730 rostri muscle of pig, 311

Descemet, membrane of, 742

Descent of testicles, 490

Descriptive terms, 18

Diagonal fissure of ox, 716 of pig, 721

Diameter, conjugate, of pelvis, 97 of ox, 132 sacro-pubic, of pelvis, 97 transverse, of pelvis, 97

Diaphragm of dog, 325 of horse, 243 of ox, 300 of pig, 313

Diaphragma sellæ, 646

Diaphragmatic flexure, 366 lobe of lung of ox, 463 pleura, 451 vertebra, 42

Diarthroses, 170

Diencephalon, 664

Digastric muscles, 213 nerve, 685

Digastricus muscle, 222 of dog, 319 of ox, 297 of pig, 311

Digestive system, 330 of dog, 423 of ox, 382 of pig, 410 of sheep, 405

Digit or digits, 28 of dog, 165, 780 extensor muscles of, 322, 328 of horse, fascia of, 263 muscles of, 295 of ox, 130, 775 of pig, muscles of, 315

Digital artery, 564 common, 563 of ox, 620 external, of ox, 614, 620 of dog, 641, 637 of pig, 629, 630 volar, of ox, 614 bones, 28, 30 cushion, 771 extensor muscle, anterior, of dog, 328 of ox, 304, 309 of pig, 317 common, of dog, 322 of ox, 304 of pig, 315 internal, of ox, 304, 309 lateral, of dog, 322, 328 of ox, 304, 309 of pig, 315, 317 of ox, 304, 309 of pig, 315 fascia, 274 flexor muscle, deep, of dog, 323, 329 of ox, 305 of pig, 316 superficial, of dog, 323, 329 of ox, 305 of pig, 316 fossa of epididymis, 485 nerves of dog, 730, 732 of horse, 701 of ox, 718, 719 of pig, 723 pads, 780

Digital veins, 595 of dog, 642, 643 of ox, 621, 623

Dilatator naris apicalis muscle of ox, 296 inferior muscle of horse, 218 of ox, 296 lateralis muscle of horse, 217 of ox, 295 of pig, 311 superior muscle of horse, 218 of ox, 296 transversus muscle of horse, 217 of pig, 311 pupillæ, 744

Diploë, 21

Diploic veins, 593

Discs, articular, 171 of temporo-mandibular articulation, 179

Distal interphalangeal joint of horse, 189 sesamoid bones of ox, 131

Diverticulum duodeni of horse, 362 nasi of horse, 436 preputial, of pig, 506 suburethral, of cow, 519 of sow, 522 tubæ auditivæ, 756 ventriculi of stomach of pig, 418

Dolichocephalic breed of dogs, 159

Dorsal artery, 538 of dog, 633 of ox, 609 of penis, 580 of pig, 627 columns of spinal cord, 651 common ligament of carpal joints, 183 flexion of joints, 171 groove of third phalanx, 91 ligaments of hock joint, 201 of interphalangeal joints of dog, 209 plexus, 595 sacro-iliac ligament, 190 sesamoids of dog, 165 vein, 586

Dorso-intercostal artery, 538

Dorso-scapular ligament of horse, 235

Dorsum of tongue of horse, 335

Duct or ducts, alveolar, of lungs, 457 Bartholin’s, of mare, 515 bile, common, of sheep, 410 of ox, 398 of pig, 419, 422 cystic, of ox, 403 ejaculatory, 488, 492, 499 hepatic, 376 lacrimal, 737 lactiferous, of cow, 521 of mare, 516 lymphatic, right, 601 naso-lacrimal, 436, 737 of ox, 773

Ducts of bulbo-urethral glands, 494, 499 of epididymis, 487 of mammary glands of mare, 516 of pancreas, 372 of prostate, 493 orbital, of dog, 427 pancreatic, accessory, of dog, 431 of horse, 373 of dog, 431, 434 of horse, 372 of ox, 398 of pig, 419, 423 parotid, of dog, 423, 427 of horse, 347 of pig, 411, 414 prostatic, of horse, 499 of ox, 502 Santorini’s, of horse, 373 sublingual, of dog, 427 of horse, 348 submaxillary, of dog, 427 of horse, 348 thoracic, of dog, 643 of horse, 600 of pig, 630 tracheal, 603 Wirsung’s, of horse, 372

Ductus arteriosus, 535, 607 endolymphaticus, 759 reuniens, 759 sublingualis major, of pig, 416 minores, of pig, 416 utriculo-saccularis, 759 venosus, 607 of ox, 403

Duodenal angle of horse, 372 glands of horse, 363

Duodenum of horse, 360 of ox, 398

Dura mater, 645 spinal, 646

Ear, external, of horse, 747 internal, of horse, 758 middle, of horse, 752 of dog, 779 of horse, 747 of ox, 774 of pig, 778

Ectolateral fissure of dog, 727

Ectomarginal fissure, 669 of dog, 726 of ox, 716 of pig, 721

Ectosylvian fissure of dog, 726

Ectoturbinals of ethmoid of horse, 52

Eighth nerve, 686

Ejaculatory ducts, 488, 492, 499

Elastic membrane of trachea, 449

Elbow joint of dog, 205 of horse, 181 of ox, 205 of pig, 205

Eleventh nerve, 690

Embryology, 17

Eminence, frontal, of ox, 118

Eminence, ilio-pectineal, of pubis, 95 intercondyloid, of tibia, 101 olivary, of dog, 725

Eminentia conchæ, 748 medialis, 662 pyramidalis, 755

Emissary veins, 591

Enamel of teeth, 339

Enarthrosis, 172

Encephalon of horse, 652

End-arteries, 524

End-brain, 667

Endocardium, 530, 534

Endothoracic fascia, 450

Endoturbinals of ethmoid, 52

Ensiform cartilage, 46

Entomarginal fissure of dog, 727 of horse, 669 of ox, 716 of pig, 721

Epicardium, 525, 534

Epicondyle, external, of femur, 100 of humerus, 80 internal, of femur, 100 of humerus, 80

Epidermis, 761 of dog, 780

Epididymis of dog, 506 of horse, 485 structure of, 485 of ox, 500 of pig, 504

Epidural space, 646

Epigastric zone of horse, 353

Epiglottis of dog, 467 of horse, 442 of ox, 459 of pig, 411, 465

Epihyoids of horse, 65

Epiphyseal cartilage, 22

Epiphysis, 665

Epiploic foramen, 379 of ox, 396

Epithelium, corneæ, 741 germinal, of ovary, 510 of Fallopian tubes, 511

Equator of eye, 740

Erectile tissue of urethra, 499

Erector clitoridis muscle, 515 penis muscle, 496

Ergot, 771

Esophageal membrane, 360

Esophagus. See Œsophagus.

Ethmoid artery, 554 bone of dog, 157 of horse, 52 development of, 52 of ox, 116 of pig, 142 sinus, 74

Ethmoidal cells, 52 foramen, 51, 52, 67, 70 fossa, 52, 70 meatuses, 52 of nasal cavity, 440 nerve, 678 of dog, 728

Ethmo-turbinals, 52

Eustachian tube, 348, 755 of dog, 780 of ox, 775

Eustachian tube of pig, 778 osseous, 57

Excavatio pupillæ nervi optici, 745

Excretory ducts, 737

Exoskeleton, 19

Extension of joints, 171

Extensor brevis muscle of ox, 310 carpi muscle of dog, 322 obliquus muscle, of dog, 322 of horse, 267 of ox, 304 of pig, 315 radialis brevis muscle of dog, 322 longus muscle of dog, 322 muscle of horse, 263 of ox, 304 of pig, 315 ulnaris muscle of dog, 323 of horse, 268 digitalis brevis muscle of dog, 328 of pig, 317 communis muscle of dog, 322 of horse, 263 lateralis muscle of dog, 322 of horse, 265 of leg of horse, 288 longus muscle of leg of horse, 288 digiti quinti muscle of dog, 323 tertii et quarti muscle of dog, 323 fossa of femur of horse, 100 hallucis longus muscle of dog, 328 of pig, 317 indicis proprius muscle of pig, 315 metacarpi obliquus muscle of horse, 267 muscle of digits of dog, 322, 328 pedis brevis muscle of horse, 295 muscle of horse, 264, 288

External angle of ilium, 94 of pubis, 96 auditory meatus, 56 process, 56, 67 condyle of humerus, 80 cremaster muscle, 249, 490 epicondyle of femur, 100 of humerus, 80 frontal crest, 55 inguinal ring, 246, 250 intercostal muscles of dog, 325 of horse, 240 of pig, 313 interosseous muscle of horse, 273 lateral ligament of carpal joints, 183 of coffin joint, 189 of elbow joint, 182

External lateral ligament offemoro-tibial articulation, 197 of fetlock joint, 185 of hock joint, 200 of pastern joint, 188 ligament of temporo-mandibular articulation, 179 malleolus of tibia, 101 metatarsal bone, 111 oblique muscle of abdomen, 246 occipital protuberance, 50 patellar ligament, 195 pterygoideus muscle, 220 sagittal crest, 54, 66 supracondyloid crest of humerus, 80 trochanter of femur, 99 tuberosity of humerus, 78 of radius, 81 urethral orifice of cow, 519 of horse, 499 of mare, 515 of ox, 503

Eye of dog, 779 of horse, 734 of ox, 772 of pig, 777

Eyeball of dog, 779 of horse, 739 of ox, 773 of pig, 778

Eyelashes, 735 of pig, 777

Eyelid of dog, 779 of horse, 735 muscles of, 218 of ox, 772 of pig, 777 structure of, 736 third, 736 of ox, 772 of pig, 777

Face, bones of, of dog, 157 of horse, 57 of ox, 120 of pig, 142 of dog, muscles of, 318 of ox, muscles of, 295

Facets, anterior, of larynx, 441 costal, of thoracic vertebræ, 36, 37 of tibia, 102 of ulna, 83 posterior, of larynx, 441

Facial artery, 547 of dog, 635 transverse, 550 bones, 27 canal, 56 crest, 58, 62, 68 nerve, 684 of dog, 729 of ox, 717 nucleus, 684 panniculus of pig, 311 tuberosity of ox, 120 veins, 588 of pig, 630

Facies articulares arytænoideæ, 441

Facies articulares thyreoideæ, 441 costalis, 454 diaphragmatica, 456 mediastinalis, 454

Falciform ligament, 374

Fallopian tubes of bitch, 522 of cow, 517 of mare, 511 structure of, 511 of sow, 522

False nostril of horse, 436 ribs, 25, 43 vertebræ, 24 vocal cords of dog, 467 of horse, 447

Falx cerebri, 645

Fascia, 211, 212 abdominal, deep, 245 superficial, 245 buccal, 213 carpal, 263 coccygeal, 238 common, of leg, 274 crural, 274 deep, 212 of head, 213 digital, 274 endothoracic, of horse, 450 femoral, internal, 274 gluteal, 273 iliac, 273 lata of gluteal region, 273 lumbo-dorsal, 235 metatarsal, 274 of back, 235 of forearm, 262 of head, 213 of horse, 213 of loins, 235 of mammary glands, 516 of manus, 262 of metacarpus, 263 of neck, 224 of pelvic limb, 273 of shoulder of horse, 255 of tail, 238 orbital, 738 pectoral, 252 pelvic, 273 pharyngeal, 213 propria of neck, 224 scrotal, 488 superficial, 212 of gluteal region, 273 of head, 213 tarsal, 274 temporal, 213 transversalis, 249

Fasciculus, cerebello-olivary, 658 cerebellospinal, 661 cerebrospinal, 660 cuneatus, 652 dorsal longitudinal, 658, 660 gracilis, 652 intracommissuralis ventralis, 652 nucleo-cerebellar, 661 pedunculo-mammillaris, 665 pyramidal, 660 thalamo-mammillaris, 665

Faucial tonsil, 333

Femoral artery, 579 anterior, 580 deep, 580 of dog, 639 of ox, 619 of pig, 630 posterior, 580 canal, 282 fascia, internal, 274 layer of external oblique muscle, 246 nerve of horse, 706 vein, 598 of dog, 642

Femoro-patellar articulation, 194 ligaments, lateral, 195

Femoro-popliteal artery, 580 vein, 598

Femoro-tibial articulation, 196

Femur, 29, 97 development of, 100 of dog, 167 of ox, 133 of pig, 148

Fenestra cochleæ, 753 ovalis, 753 rotundum, 753 vestibuli, 753, 758

Ferrein’s pyramid, 473

Fetlock joint, 185, 764

Fibers of heart, 534 of stomach, 359

Fibræ arcuatæ externæ, 657 zonulares, 747

Fibro-cartilage, accessory, of patella, 105 intervertebral, 173

Fibrous capsule of liver, 376 layer of articulations, 170 of pericardium, 525 ring of heart, 534 of intervertebral fibro-cartilages, 173 tunic of eye, 740

Fibula, 29 of dog, 168 of horse, 104 development of, 104 of ox, 134 of pig, 149

Fibular tarsal bone, 106 ligaments of, 202 of ox, 134 sustentaculum tali of, 106 tuber calcis of, 106

Fifth nerve of horse, 677 spinal root of, 658

Fila lateralis pontis, 661 radicularia, 651

Filiform papillæ of tongue of horse, 336

Fillet, 658 lateral, 660 medial, 660 terminale of horse, 648, 649

Fimbria of brain, 669 of Fallopian tubes, 511 ovaricæ of mare, 511

First carpal bone, 85 intertarsal sac, 200 nerve of horse, 676 phalanges of dog, 165

First phalanges of horse, 89, 111 development of, 89 of ox, 130 tarsal bone, 109 of ox, 135

Fissura calloso-marginalis, 669 ectomarginalis, 669 entomarginalis, 669 lateralis Sylvii, 668 marginalis, 669 mediana ventralis, 649 sublimbica, 669 thyreoidea of dog, 467 transversa, 669

Fissure, ansate, of dog, 726 calloso-marginal, 669 of dog, 727 of ox, 716 of pig, 721 central, of dog, 726 of horse, 668 of ox, 716 chorioid, 670 collateral, of dog, 726 coronal, of dog, 726 of ox, 716 of pig, 721 crucial, of ox, 717 cruciate, of dog, 727 of pig, 721 diagonal, of ox, 716 of pig, 721 ectolateral, of dog, 727 ectomarginal, 669, 721 of dog, 726 of ox, 716 ectosylvian, of dog, 726 entomarginal, of dog, 727 of horse, 669 of ox, 716 of pig, 721 genual, of ox, 717 of pig, 721 Glaserian, of horse, 57 lateral, of cerebrum, 667 of dog, 726 of horse, 668 of ox, 716 of pig, 721 longitudinal, of brain, 667 marginal, of horse, 669 of ox, 716 of pig, 721 naso-maxillary, of horse, 73, 439 of lungs of ox, 462 of Sylvius, 667, 668 of dog, 726 of ox, 716 of pig, 721 orbital, 51 petro-tympanic, 57 portal, of dog, 433 of horse, 373 of ox, 402 præsylvian, 669 of dog, 727 of horse, 669 of pig, 721 splenial, of pig, 721 sublimbic, 669 suprasplenial, of dog, 727 suprasylvian, of dog, 726 of horse, 668

Fissure, suprasylvian, of ox, 716 of pig, 721 transverse, 669 of ox, 716 umbilical, 374 ventral median, 249

Fixed vertebræ, 24

Flat muscles, 211

Flexion of joints, 171

Flexor brachii muscle of horse, 259 carpi externus muscle of horse, 268 of pig, 316 internus muscle of dog, 323 of horse, 267 of pig, 315 medius muscle of dog, 323 of horse, 268 of pig, 315 digitalis pedis muscle of dog, 329 digiti quinti muscle of dog, 324 hallucis brevis muscle, 329 longus muscle, 329 muscle, deep, of ox, 311 superficial, of ox, 311 of carpus of ox, 305 pedis perforatus muscle of horse, 271, 292, 293 perforans muscle, 271 perforatus muscle, 269 pollicis brevis muscle, 324

Flexure, diaphragmatic, 366 gastro-hepatic, 366 pelvic, 366 sigmoid, 503 sternal, 366

Floating ribs, 25

Floccular fossa of temporal bone of dog, 156

Floor of mouth of horse, 334

Fœtal circulation, 606 lung of horse, 454

Fold, alar, 437 cæco-colic, 367 deferential, of testicles, 491 gastro-pancreatic, 358 of articulations, 170 rumino-reticular, 393 sagittal, of pleura, 452 turbinal, inferior, 440 superior, 440 urogenital, 355 valvular, of cæcum, 365

Folia cerebelli, 661

Foliate papillæ of tongue, 336

Follicle, Graafian, of mare, 510 hair, 763 lymph, 600 of small intestine of horse, 363 of thyroid gland of horse, 458

Foot of horse, muscles of, 287 of ox, muscles of, 309 of pig, muscles of, 317

Foramen, alar, 68 alare, 34 cæcum of medulla, 655 carotid, of dog, 156 ethmoidal, 51, 52, 67, 70

Foramen, hypoglossal, 48, 68, 71 incisive, 59, 69 infraorbital, 58, 68 interventricular, 667, 674 intervertebral, of horse, 33 of ox, 112 lacerum basis cranii, 57, 68, 71 of horse, 49 orbitale of horse, 51, 67 magnum of horse, 48, 68 mandibular, 64 maxillary, 58, 67 mental, 63 nutrient, of femur, 97 of humerus, 78 of ilium, 94 of metacarpus, 88 of tibia, 100 obturator, of dog, 167 of horse, 96 of ox, 132 of Monro, 667, 674 optic, of horse, 50, 51, 67, 70 orbital, internal, 67, 70 ovale, 607 of horse, 530 of ox, 115 palatine, posterior, 58, 68 pathetic, 67 pterygoid, 51, 68 rotundum, 51, 67 sacral, 40 inferior, of ox, 114 sciatic, great, of horse, 94 singulare, 759 sinistrum, 244 sphenopalatine, 58, 60, 67, 71 stylo-mastoid, 57 supraorbital, of horse, 55, 66 of ox, 119 supratrochlear, of humerus of dog, 163 temporal, of horse, 51, 67 thyreoideum, 442 transversarium of axis of ox, 112 venæ cavæ, of horse, 245 volar, of third phalanx, 91 Winslow’s, of horse, 379 of ox, 396

Foramina papilloma of kidney of ox, 480

Forearm, bones of, 28 of horse, fasciæ of, 262 deep, 262 superficial, 262 muscles of, 262 of ox, muscles of, 304 of pig, muscles of, 315

Forefoot, bones of, 28

Foretop, 764

Formatio reticularis, 651, 660

Fornix, 673 conjunctivæ, 736 vaginæ of mare, 514

Fossa, acetabular, 96 anterior, of skull, 70 atlantis of, 34 condyloid, of horse, 48, 68 coronoid, of horse, 80 digital, of epididymis, 485 ethmoidal, 52, 70

Fossa, extensor, of femur, 100 floccular, of temporal bone of dog, 156 glandis of penis, 495 glenoid, 56 hyaloidea, 746 hypophyseal, 50 infraspinous, 75 infratemporal, 68 intercondyloid, anterior, of tibia, 102 of femur, 99 posterior, of tibia, 102 interpeduncularis, 664 masseteric, of mandible of dog, 159 middle, of skull, 71 ovulation, of mare, 509 ovalis, 607 of horse, 530 of Sylvius, 667 olecranon, 80 olfactory, 52, 70 pituitary, 50 posterior, of skull, 71 postglenoid, 56 pterygo-palatine, 60, 67 subscapular, 75 supracondyloid, of femur of horse, 99 supraspinous, 75 synovial, of tibial tarsal bone, 105 temporal, 67 transverse, 658 trochanteric, of femur, 99 synovial, 170 vaginæ of mare, 514

Fourth carpal bone of horse, 86 metatarsal bone of horse, 111 nerve of horse, 677 tarsal bone of horse, 109 of ox, 134 ventricle of horse, 662

Fovea capitis of femur of horse, 99 nasalis, 662 trochlearis of horse, 55

Frænula labii of horse, 331

Frenum linguæ of horse, 334, 335 of pig, 411 preputial, of horse, 497

Frog matrix, 770 of hoof, 767 sensitive, 770 structure of, 769

Frog-stay, 767

Frontal artery, 553 bone of dog, 155 of horse, 55 of ox, 118 of pig, 141 crest of horse, 55, 66 eminence of ox, 118 nerve of dog, 728 of horse, 678 of ox, 717 process of dog, 157 region of skull of horse, 66 sinus of dog, 161 of horse, 55, 73

Frontal sinus of ox, 125 of pig, 145 surface of skull of horse, 65 of ox, 123 suture of horse, 55 vein of ox, 621

Frontalis muscle of ox, 295

Fronto-lacrimal sutures of horse, 55

Fronto-maxillary opening of horse, 73

Fronto-scutularis, 749

Fundus glands of stomach of horse, 360

Fungiform papillæ of tongue of horse, 336

Funiculi dorsales, 651 ventrales, 651

Furca ungulæ, 767

Gall-bladder of dog, 434 of ox, 403 of pig, 422

Ganglia, cervical, of ox, 720 cœliaco-mesenteric, 714 definition of, 644 sacral, of ox, 720 thoracic, of ox, 720

Ganglion, cervical, 711 of dog, 733 of pig, 724 ciliary, 679, 711 of ox, 717 coccygeal, 713 Gasserian, 678 impar, 713 jugular, 687 of dog, 729 of ox, 717 of pig, 722 lumbar, 713 mesenteric, 714 nodosum of dog, 729 of ox, 717 of pig, 722 otic, 681, 711 of ox, 717 petrous, 686 semilunar, 678 sphenopalatine, 711 spinal, 692 spirale, 761 thoracic, 712 vestibular, 686

Gartner, canals of, of vagina of cow, 519

Gasserian ganglion, 678

Gastric artery, 506 of dog, 638 lymph glands, 604 of ox, 626 of pig, 632 plexus, 714 of dog, 729 vein, 597

Gastrocnemius muscle of dog, 329 of horse, 290 of ox, 311 of pig, 317

Gastro-colic omentum of horse, 358

Gastro-duodenal artery, 569

Gastro-duodenal vein, 597

Gastro-epiploic artery, 569, 570

Gastro-hepatic artery of pig, 627 flexure of horse, 366 omentum of horse, 354, 358

Gastro-pancreatic fold of horse, 358

Gastro-phrenic ligament of horse, 358

Gastro-splenic artery of dog, 638 omentum of horse, 354, 358, 379

Gemellus muscle of horse, 284 of ox, 308 of pig, 317

Geniculate body, internal, 665 of dog, 725 of ox, 716

Genio-glossus muscle of horse, 338

Genio-hyoideus muscle of ox, 298

Genital organs, 469 female, 508 male, 485 of dog, 506 of horse, 485 of ox, 500 of pig, 504 of bitch, 522 of cow, 517 of mare, 508 of sow, 521

Genito-hyoideus muscle of horse, 223

Genu of corpus callosum, 672

Genual fissure of ox, 717 of pig, 721

Germinal epithelium of ovary of mare, 510

Ginglymus, 172

Girdle, pelvic, 29 of horse, 92 shoulder, 27 of horse, muscles of, 250 of ox, muscles of, 302 of pig, muscles of, 314

Glands or gland, anal, of dog, 432 buccal, of horse, 332 of ox, 383 of pig, 410 bulbo-urethral, of dog, 506 of horse, 493 of ox, 503 of pig, 505 cardiac, of stomach of horse, 360 carpal, 778 ceruminous, 749 circumanal, of dog, 432 Cowper’s, of dog, 506 of horse, 493 of ox, 503 of pig, 505 duodenal, of horse, 363 fundus, of stomach of horse, 360 hæmolymph, 600 labial, of horse, 332 lacrimal, of dog, 779 of horse, 737 Glands, lacrimal, of ox, 773 lingual, of horse, 336 lymph, 599 bronchial, of horse, 457 of ox, 623 of pig, 630 mammary, of bitch, 523 of cow, 519 of mare, 516 of sow, 522 molar, of ox, 383 mucous, of larynx of horse, 448 of trachea of horse, 450 nasal, of horse, 440 of Bartholin of cow, 519 of Bowman, 772 of Henle, 736 of rectum of horse, 370 of skin, 762 of small intestine of horse, 362 of uterus of cow, 518 olfactory, of horse, 440 orbital, of dog, 427 palatine, of horse, 333 parathyroid, of dog, 468 of horse, 458 of ox, 464 parotid, of dog, 427 of horse, 346 of ox, 388 of pig, 414 preputial, of horse, 497 prostate, of dog, 506 of horse, 493 of ox, 502 of pig, 505 pyloric, of stomach of horse, 360 salivary, of dog, 427 of horse, 346 of ox, 388 of sheep, 407 sebaceous, 762 of dog, 780 of ox, 775 of pig, 778 solitary, of rectum of horse, 370 of small intestine of horse, 363 of pig, 420 sublingual, of dog, 427 of horse, 348 of ox, 388 of pig, 415 submaxillary, of dog, 427 of horse, 347 of ox, 388 of pig, 415 sudoriferous, 762 suprarenal, of horse, 477 sweat, 762 of dog, 780 of ox, 775 of pig, 778 tarsal, 735 thymus, of dog, 468 of horse, 458 of ox, 464 of pig, 466 thyroid, of dog, 468 of horse, 457

Glands, thyroid, of ox, 464 of pig, 466 urethral, of horse, 499 uterine, of cow, 518 of mare, 513 zygomatic, of dog, 427

Glandula laryngeæ of horse, 448 palpebræ tertiæ profunda, 779 tympanicæ, 755 vestibulares majores of cow, 519 of mare, 515 minores of mare, 515

Glans clitoridis of dog, 519 of mare, 515 penis of dog, 506 of horse, 495 of ox, 503

Glasserian fissure of horse, 57

Glenoid cavity of horse, 67, 68, 76 fossa of horse, 56 notch of horse, 76

Gliding joint, 172 movement of joints, 171

Glomerulus of kidney of horse, 474

Glosso-pharyngeal nerve, 686

Glottis of horse, 447 vocalis of horse, 448

Gluteal artery, anterior, 577 of dog, 641 of ox, 619 posterior, 575 fascia of horse, 273 line of horse, 93 nerve of horse, 706

Gluteo-biceps muscle of horse, 278

Gluteus accessorius muscle of horse, 278 medius muscle of dog, 326 of horse, 277 of ox, 306 of pig, 316 profundus muscle of dog, 326 of horse, 278 of ox, 306 of pig, 316 superficialis muscle of dog, 326 of horse, 277 of ox, 306 of pig, 316

Goll’s column, 652

Gomphosis, 169

Graafian follicles of mare, 510

Gracilis muscle of dog, 328 of horse, 281 of ox, 308 of pig, 316

Granula iridis, 744

Gray commissure of cord of horse, 650 matter of nervous system, 644

Great colon of horse, 365. See also Colon, great. cornua of horse, 65 mesentery of horse, 354, 362

Great oblique muscle of abdomen of horse, 246 omentum of horse, 354, 358 of ox, 396 sciatic foramen of horse, 94 trochanter of femur of horse, 99

Groove, bicipital, of humerus of horse, 79 carpal, of horse, 86 coronary, of heart of horse, 527 of rumen of ox, 392 dorsal median, in horse, 649 of third phalanx of horse, 91 dorso-lateral, in horse, 649 lacrimal, of horse, 58 longitudinal, of heart of horse, 528 musculo-spiral, of horse, 77 œsophageal, of ox, 394 of sheep, 408 of heart of horse, 527 of radius of horse, 82 of sacrum of ox, 114 of tibia of horse, 102 optic, of horse, 50 palatine, of horse, 59, 69 sagittal, of horse, 54 subpubic, of horse, 95 supraorbital, of ox, 119 urethral, of horse, 495 vertebral, of horse, 42

Gross anatomy, 17

Gubernaculum testis of horse, 491

Gudden’s commissure, 666

Gums of horse, 332

Gustatory cells, 772 hair, 772 organs of dog, 781 pore, 772

Guttural pouches, 756 region of horse, 68

Gyri, cerebellar, 661 cerebral, 668 of ox, 716 of pig, 721

Gyrus dentatus, 669 subcallosal, 671

Hæmal arches of coccygeal vertebræ of dog, 152 spine, 25

Hæmolymph glands, 600

Hæmorrhoidal artery, 574 of dog, 641 nerve of horse, 710

Hair, gustatory, 772

Hair-follicle, 762

Hairs, 762 of horse, 764 of ox, 775 of pig, 778 tactile, 763

Hamulus of horse, 61

Hand. See Manus.

Hard palate of dog, 423 of horse, 69, 332 of ox, 383 of pig, 411

Hard palate of sheep, 405

Harder’s gland, 777

Head of horse, fasciæ of, 213 muscles of, 213 of pig, muscles of, 311

Heart, 524 of dog, 632 of horse, 526 structure of, 534 of ox, 608 of pig, 626 veins of, 585

Heels, 764

Helicis muscle, 752

Helicotrema, 759

Hemispheres, cerebellar, 660 cerebral, 667 of dog, 726 of ox, 716 of pig, 721

Henle, glands of, 736

Hepatic artery, 567 of dog, 638 of horse, 377 of ox, 614 duct of horse, 376 lymph glands, 605 of ox, 626 of pig, 632 plexus, 714 of horse, 377 veins, 596 of horse, 377

Hepato-renal ligament of horse, 375

Hiatus aorticus of horse, 244 œsophageus of horse, 244

Hilus of lungs of horse, 454 of ovary of mare, 510 of spleen of horse, 378 renalis, of horse, 470

Hinge-joint, 172

Hip joint of horse, 192 of ox, 209 of pig, 209

Hippocampal commissure, 670

Hippocampus, 669

Histology, 17

Hock, 29 capped, 293 joint of dog, 210 of horse, 199 of ox, 210 of pig, 210 of horse, 105 of ox, 134 of pig, 149

Hoof of horse, 764 matrix of, 769 structure of, 768

Horn-cores of ox, 118

Horner’s muscle, 736

Horns of lateral ventricle, 674 of ox, 776

Humeralis obliquus muscle of horse, 260

Humerus, 28 of dog, 162 of horse, 77 development of, 80 of ox, 127 of pig, 146

Humor, aqueous, 746

Humor, vitreous, 746

Hydatid of Morgagni of Fallopian tubes of mare, 511 of testicles of horse, 485

Hymen of mare, 514

Hyo-epiglottic ligament, 444

Hyo-epiglotticus muscle, 445

Hyo-glossus muscle, 338

Hyoid bone of dog, 159 of horse, 64 of ox, 122 of pig, 144 muscle of dog, 319 of horse, 222 of ox, 297 process of horse, 57

Hyoidean articulations, 180

Hyoideus transversus muscle, 224 of ox, 298

Hyo-pharyngeus muscle, 350

Hyo-thyreoideus muscle, 445

Hyperdactylism, 29

Hypogastric arteries, 573 plexus, 715 vein, 597 zone, 353

Hypoglossal foramen, 48, 68, 71 nerve, 692 of dog, 730 of ox, 717 of pig, 722 nucleus, 692

Hypophyseal fossa of horse, 50

Hypophysis, 653, 665

Ileal artery, 570

Ileo-cæcal artery, 570 orifice, 364 value of dog, 431 of horse, 362, 364

Ileo-cæco-colic artery of ox, 617

Ileum, 361

Iliac artery, circumflex, 578 of dog, 639 external, 578 of ox, 619 internal, 573 of ox, 618 fascia, 273 layer of oblique muscle of abdomen, 246 lymph glands, 604 of dog, 643 of ox, 625 of pig, 631 vein, common, 597 external, 597 internal, 597 of dog, 642

Iliaco-femoral artery, 577 of ox, 619 vein, 598

Iliacus muscle of dog, 326 of horse, 275 of ox, 306

Iliocostalis cervicis muscle of horse, 227 muscle of horse, 236 of ox, 300

Iliohypogastric nerve of horse, 704

Ilio-inguinal nerve of horse, 704

Ilio-lumbar artery, 577 of dog, 641 of ox, 619 of pig, 630 ligament of horse, 191 vein, 597

Ilio-pectineal line of horse, 93

Ilio-psoas muscle of horse, 275

Ilio-pectineal eminence of pubis, 95

Ilium, 29 of dog, 165 of horse, 93 of ox, 131 of pig, 148

Impression, cardiac, of lungs, 454

Incisive foramen, 59

Incisivus inferior muscle of horse, 216 of ox, 295 superior muscle, 216

Incisor artery, 552 teeth, 338, 341 deciduous, of ox, 386 of dog, 425 of ox, 386 of pig, 412 of sheep, 405

Incisura intertragica, 748 thyreoidea caudalis, 442

Incus, 754

Index, cephalic, of dog, 159 cranio-facial, of dog, 159

Inferior angle of scapula, 76 atlanto-axial ligament, 176 atlanto-occipital membrane, 176 border of mandible, 64 check ligament of carpal joints, 183 of deep digital flexor muscle, 272 commissure of vulva, 515 common vertebral ligament, 173 dental canal, 64 dilatator naris muscle, 218 incisivus muscle, 216 interdigital ligaments of ox, 208 ischiatic spine, 95 maxillary foramen, 64 sinus, 73 meatus of nasal cavity of dog, 467 of horse, 439 of pig, 465 of nose, 62, 72 navicular ligament, 190 sacral foramen of ox, 114 sacro-coccygeus muscle, 240 sesamoidean ligaments, 188 thyro-arytenoid ligament, 444 turbinal bone of dog, 158 of horse, 62 of ox, 122 crest, 58 fold of horse, 440

Infraorbital artery, 555 of dog, 635 of pig, 627 canal, 59 foramen, 58, 68 nerve of dog, 728 of horse, 681 of pig, 722 pouch, 777 vein, 589

Infraspinatus muscle of dog, 321 of horse, 256 of ox, 302 of pig, 314

Infraspinous fossa, 75

Infratemporal fossa, 68

Infratrochlear nerve of dog, 728 of horse, 679

Infundibular recess, 667

Infundibulum, 653 of Fallopian tubes, 511 of incisor teeth, 341

Inguinal canal, 249 ligament, 246 lymph glands, 604 of dog, 643 of ox, 625 of pig, 632 pouch of sheep, 777 ring, external, 246, 250 internal, 248, 249

Inlet of pelvis of dog, 167 of horse, 96 of ox, 132 of pig, 148 of thoracic cavity, 450

Inscriptiones tendineæ of rectus abdominis of horse, 248

Insertion of muscles, 212

Interalveolar septa, 58 space, 58, 69

Interarytenoid cartilage of larynx of dog, 467 of pig, 465

Interbrain, 664

Intercarpal joint, 183 sac, 183

Intercentral articulations of vertebræ, 173

Interchondral ligaments, 178

Intercondyloid fossa, anterior, of tibia, 102 eminence of tibia, 101 fossa of femur, 99 posterior, of tibia, 102

Intercornual articulation of horse, 180

Intercostal arteries, 565 of ox, 614 of pig, 627 lymph glands, 603 muscles, external, of dog, 325 of horse, 240 of pig, 313 internal, of horse, 242 of pig, 313 nerves of horse, 702 spaces, 25 veins, 587

Interdental space of horse, 58

Interdigital ligaments, inferiorm of ox, 208

Interdigital ligaments, superior, of ox, 206 pouch, 777

Interlobular bronchi of horse, 457 tissue of lungs, 457

Intermediate carpal bone of horse, 83 zone of kidney, 473

Intermetacarpal joints of dog, 206 of ox, 206 of pig, 206

Intermuscular septa, 212 of forearm, 262 of gluteal region, 273, 274 of leg, 274 of shoulder, 255

Internal angle of ilium, 94 of pubis, 95 auditory meatus, 56 capsule, 665, 676 ondyle of humerus of horse, 79 digital extensor muscle of ox, 304, 309 ear of horse, 758 epicondyle of femur, 100 of humerus, 80 femoral fascia, 274 flexor muscle, 267 inguinal ring, 248, 249 intercostal muscles, 242 of pig, 313 interosseous muscle, 273 lateral ligament of carpal joints, 184 of coffin joint, 189 of elbow joint, 181 of femoro-tibial articulation, 197 of fetlock joint, 185 of hock joint, 201 of pastern joint, 188 malleolus of tibia, 103 metatarsal bone, 111 muscles of thigh of ox, 308 oblique muscle of abdomen, 247 occipital protuberance, 54 orbital foramen, 67, 70 patellar ligament, 196 pterygoideus muscle, 219 sagittal crest, 54 trochanter of femur, 97 tubercle of humerus, 78 tuberosity of humerus, 79 of radius, 81 urethral orifice of horse, 477 of mare, 499

Interneural articulations of vertebræ, 173

Interosseous artery, common, 561 dorsal, 562 of dog, 635 of ox, 612 recurrent, 561 ligament of radio-ulnar articulation, 182 medius muscle of ox, 305 membrane of tibio-fibular articulation, 199 muscles of dog, 324, 329

Interosseous muscles of horse, 273, 295 plexus, 595 space of forearm, 80 of leg, 29 vein, 595

Interparietal bone of dog, 155 of horse, 53 of ox, 116 of pig, 140 suture of horse, 54

Interpeduncular space, 664

Interphalangeal articulation, distal, 189 proximal, 188 joints of dog, 209 of ox, 208 of pig, 208

Interscutularis, 749 of dog, 780 of ox, 774

Intersesamoidean ligament, 187

Interspinales muscles of dog, 325 of ox, 300 of pig, 313

Interspinous ligaments of horse, 175, 176

Interstitial tissue of mammaryglands, 516

Intertarsal sac, first, 200 second, 200

Intertransversales caudæ, 239 colli muscle, 228 lumborum muscle, 238, 276 muscle of dog, 324, 325 of ox, 300 of pig, 312, 313

Intertransverse articulations, 175 ligaments, 175

Intertubercular groove of humerus, 79

Interventricular foramen, 667, 674 grooves of heart, 528 septum of left ventricle, 534

Inervertebral fibro-cartilages, 173 foramen, 33 of ox, 112 foramina, 25

Intestinal arteries, 570

Intestine, large, of dog, 433 of horse, 363 of ox, 398 of pig, 420 of dog, 430 of ox, 397 of pig, 419 of sheep, 409 small, of dog, 430 of horse, 360 of ox, 398 of pig, 419 of sheep, 409

Intima of arteries, 525 of veins, 525

Intraarticular ligaments, 171

Intumescentia cervicalis of horse, 648 lumbalis, 648

Iris of dog, 779

Iris of horse, 744 of ox, 774 of pig, 778

Ischiatic artery, 575 of ox, 619 lymph glands, 604 of ox, 626 of pig, 632 spine, inferior, of horse, 95 superior, of horse, 94, 95

Ischio-cavernosus muscle of clitoris, 515 of penis, 496 of ox, 503

Ischio-coccygeus muscle, 238

Ischio-femoralis muscle, 283

Ischio-urethral muscles of horse, 499

Ischium, 29 of dog, 165 of horse, 95 of ox, 131 of pig, 148

Isthmus faucium of horse, 335, 348 of ox, 385 œsophagi of dog, 428 of prostate, 493 of thyroid gland, 457 of dog, 468 of urethra masculina, 498 pharyngeal, 350

Jacobson’s organ of horse, 440

Jejuno-ileum, 361

Jejunum, 361

Joint, 169. See also Articulations.

Jugular ganglion, 687 of dog, 729 of ox, 717 of pig, 722 veins, 587 of dog, 642 of ox, 621 of pig, 630

Jugulomandibularis muscle, 222

Kerato-hyoideus muscle, 223 of ox, 298

Kerato-hyoids of horse, 65

Kerato-pharyngeus muscle of horse, 350

Kidneys, 469 of dog, 483 of horse, 469 arteries of, 475 blood-supply of, 475 cortical substance of, 473 fibrous capsule of, 473 coat of, 474 fixation of, 472 glomerulus of, 474 intermediate zone of, 473 left, 470 lobules of, 473 lymph vessels of, 475 Malpighian corpuscles, 473 pyramid of, 473 medullary substance, 473

Kidneys of horse, mucous coat of, 474 muscular coat of, 474 papilla of, 474 pelvis of, 473 right, 469 stroma of, 475 structure of, 473 tubules of, 474 veins of, 475 vessels and nerves of, 754 weight and size of, 472 of ox, 478 of pig, 481 of sheep, 480

Labia of vulva, 515 vocalis of horse, 448

Labial artery, 549 of ox, 611 superior, 550 glands of horse, 332 nerve of horse, 681 veins, 589 of ox, 621

Labyrinth, membranous, 759 of ethmoid bone, 52 osseous, 758

Lacrimal apparatus, 737 artery, 553 bone of dog, 158 of horse, 61 of ox, 121 of pig, 143 bulla of ox, 121 canal, osseous, 61 caruncle, 735 duct of horse, 737 gland of dog, 779 of horse, 737 of ox, 773 groove, 58 lake, 735 nerve of dog, 728 of horse, 678 of ox, 717 of pig, 722 pouch, 777 process of dog, 158 sac of horse, 737 sinus of ox, 126 tubercle of horse, 61

Lactiferous ducts of cow, 521 of mare, 516 sinus of cow, 521

Lacus lacrimalis, 735

Lamina basalis, 743 choriocapillaris, 743 cribrosa scleræ, 741 elastica posterior, 742 fusca, 740 limitans anterior, 741 of hoof, 765 of nostrils, 437 of omasum of ox, 395 of thyroid cartilage, 442 papyracea, 52 spiralis ossea, 759 suprachorioidea, 742 terminalis of third ventricle, 667

Lamina, transverse, of ethmoid bone of dog, 157 vasculosa, 742

Laminar matrix, 769

Laryngeal artery of ox, 610 nerve of dog, 729 recurrent, 689 superior, 689 orifice, 348 saccule, 447

Larynx of dog, arytenoid cartilage of, 467 cricoid cartilage of, 467 cuneiform cartilage, 467 interarytenoid cartilage of, 467 of horse, 440 arytenoid cartilages, 443 arytenoideus transversus muscle of, 446 cartilages of, 441 cavity of, 447 crico-arytenoideus dorsalis muscle of, 445 lateralis muscle of, 446 cricoid cartilage of, 441 facets, 441 joints of, 444 lateral ventricle of, 447 ligaments of, 444 membranes of, 444 middle ventricle of, 447 mucous glands of, 448 membrane of, 448 muscles of, 445 transverse arytenoid ligament of, 444 ventricular ligament, 444 vessels and nerves of, 448 vestibule of, 447 walls of, 441 of ox, 459 of pig, 465

Lateral cartilages of phalanges, ligaments of, 190 of third phalanx, 91 column of spinal cord, 651 digital extensor muscle of dog, 322, 328 of horse, 265 of leg of horse, 288 of ox, 304, 309 of pig, 315, 317 femoro-patellar ligaments of horse, 194 fissure of cerebrum, 667 of dog, 726 of horse, 668 of ox, 716 of pig, 721 ligament, external, of carpal joints, 183 of coffin joint, 189 of elbow joint, 182 of femoro-tibial articulation, 197 of fetlock joint, 185 of hock joint, 200 of pastern joint, 188 internal, of carpal joint, 184 of coffin joint, 189 of elbow joint, 181

Lateral ligament, internal, of femoro-tibial articulation, 197 of fetlock joint, 185 of hock joint, 201 of pastern joint, 188 left, of liver, 375 of atlanto-occipital articulation, 177 of bladder, 476 of horse, 356 right, of liver, 375 masses of ethmoid, 52 muscles of neck, 229 pterygoideus muscle, 220 rectus capitis, 228 sacro-coccygeus muscle, 239 sacro-iliac ligament, 190 sesamoidean ligaments, 187 surface of skull of dog, 160 of horse, 66 of ox, 123 of pig, 144 ventricle, 674 of larynx of horse, 447 of ox, 459

Lateralis sterni muscle of horse, 242

Latissimus dorsi muscle of dog, 320 of horse, 251 of ox, 302 of pig, 314

Layer, femoral, of external oblique muscle, 246 fibrous, of articulations, 170 of pericardium, 525 iliac, of external oblique muscle, 246 muscular, of trachea, 450 serous, of pericardium, 525 synovial, of articulations, 170 visceral, of pericardium, 525

Leg, bones of, 29 of horse, muscles of, 287 anterior, 288 posterior, 290 of ox, muscles of, 309 of pig, muscles of, 317

Lemniscus, 658 lateralis, 660 medialis, 660

Lens, crystalline, 746

Lenticular nucleus, 675

Levatores costarum muscle of dog, 325 of horse, 240 of ox, 300 of pig, 313 labii superioris proprius of dog, 318 of horse, 215 of ox, 295 of pig, 311 nasolabialis muscle of dog, 318 of horse, 214 of ox, 295 of pig, 311 palati muscle of horse, 333 palpebræ superioris, 219, 738 rostri muscle of pig, 311 scapulæ hominis, 254

Ligament or ligaments, annular, 212 anterior, of horse, 263 of manus of horse, 263 of pelvic limb of horse, 274 posterior, of carpus of horse, 263 arciform, of radio-ulnar articulation of horse, 182 arytenoid, transverse, of larynx of horse, 444 astragalo-calcaneal, 202 astragalo-scaphoid, 202 atlanto-axial, inferior, 176 superior, 176 axillary, of Helmholtz, 755 broad, of uterus of bitch, 523 of cow, 518 of horse, 356 of mare, 513 calcaneo-cuboid, 202 calcaneo-cunean, 202 calcaneo-metatarsal, 201 calcaneo-scaphoid, 202 capsular, 170 caudate, of liver, 375 check, inferior, of carpal joints of horse, 183 of deep digital flexor muscle of horse, 272 of hock joint of horse, 200 superior, of superficial digital flexor muscle of horse, 270 common vertebral, inferior, of horse, 173 superior, of horse, 173 conjugal, of horse, 177 coronary, of horse, 374 costo-sternal, superior, 178 costo-transverse, superior, 177 cotyloid, of horse, 192 crucial, of femoro-tibial articulation of horse, 198 cuboido-cunean, 202 cuboido-scaphoid, 202 dorsal common, of carpal joints of horse, 183 of hock joint of horse, 201 of interphalangeal joints of dog, 209 dorso-scapular, of horse, 235 external lateral, of carpal joints of horse, 183 of coffin joint, 189 of elbow joint, 182 of femoro-tibial articulation of horse, 197 of fetlock joint, 185 of hock joint, 200 of pastern joint, 188 of temporo-mandibular articulation, 179 falciform, of horse, 374 femoro-patellar, lateral, 195 gastro-phrenic, of horse, 358 hepato-renal, of horse, 375 hyo-epiglottic, of horse, 444 ilio-lumbar, of horse, 191 inguinal, of horse, 246 interchondral, of horse, 178

Ligament, interdigital, inferior, of ox, 208 superior, of ox, 206 internal lateral, of carpal joints of horse, 184 of coffin joint, 189 of elbow joint, 181 of femoro-tibial articulation of horse, 197 of fetlock joint, 185 of hock joint, 201 of pastern joint, 188 interosseous, of radio-ulnar articulation of horse, 182 intersesamoidean, 187 interspinous, of horse, 175, 176 intertransverse, 175 intraarticular, 171 lateral, left, of liver of horse, 375 of atlanto-occipital articulation, 177 of bladder of horse, 476 of horse, 356 right, of liver of horse, 375 long, of hock joint, 201 middle of bladder, 476 of horse, 356 navicular, inferior, 190 suspensory, of horse, 189 odontoid, of horse, 176 of auditory ossicles, 755 of fibular tarsal bone, 202 of larynx of horse, 444 of lateral cartilages of phalanges of horse, 190 of liver of horse, 374 of lung of horse, 452 of neck of rib, of horse, 177 of peritoneum of horse, 354 of scrotum of horse, 488 of tibial tarsal bone, 202 of vertebræ of dog, 204 of horse, 172 of ox, 203 of pig, 204 ovarian, of bitch, 522 of mare, 509 palpebral, 736 patellar, of horse, 195 periarticular, 171 plantar, of hock joint, 201 posterior, of pastern joint, 188 of temporo-mandibular articulation, 179 Poupart’s, of horse, 246 pubo-femoral, 193, 250 radiate, of horse, 177 round, of bladder, 476 of hip joint of horse, 193 of horse, 356 of liver of horse, 375 of uterus of bitch, 523 of cow, 518 of mare, 513 sacro-iliac, dorsal, 190 sacro-iliac, lateral, 190 ventral, 190 sacro-sciatic, of horse, 190 scaphoido-cunean, 202 scrotal, of horse, 488 sesamoidean, of horse, 186, 187, 188 of ox, 207 short, of hock joint, 201 sternal, of horse, 178 structure of, 171 subcarpal, of horse, 183 subtarsal, of horse, 200 supraspinous, of horse, 174 suspensory, of penis, 494 of spleen of horse, 379 tarso-metatarsal, 202 thyro-arytenoid, inferior, 444 superior, 444 thyro-epiglottic, 444 transverse, of carpus, 263 of hip joint of horse, 192 of radio-ulnar articulation of horse, 182 umbilical, of bladder, 476 vaginal, 212 ventricular, of larynx, 444 vocal, of horse, 444 volar, of carpal joints, 183 of pastern joint, 188 V-shaped, of horse, 188 Y-shaped, of horse, 188

Ligamenta annularia of trachea, 450 flava, 174 sternopericardiaca of ox, 608

Ligamentum arteriosum, 535, 607 crico-thyreoideum, 444 denticulatum, 647 nuchæ, 174 pectinatum iridis, 742 spirale cochleæ, 760

Limbus palpebralis, 735

Line, curved, superior, of skull, 69 gluteal, 93 ilio-pectineal, 93 popliteal, of tibia, 100 terminal, 353

Linea alba, 246

Lingual artery, 548 of dog, 634 of ox, 611 branch of ninth nerve, 687 glands, 336 nerve, 683 of dog, 729 process of horse, 65 vein, 590 dorsal, 587

Lingula, 660

Lips of dog, 423 of horse, 330 muscles of, 213 of ox, 382 of pig, 410 of sheep, 405

Liquor folliculi of mare, 510 pericardii of horse, 525 pleuræ of horse, 453

Liver of dog, 432 of horse, 373 structure of, 376 of ox, 400 of pig, 421

Liver of sheep, 409

Lobe, apical, of lungs of ox, 462, 463 cardiac, of lungs of ox, 463 caudate, of liver, 433 of ox, 402 of pig, 421 cerebellar, 661 diaphragmatic, of lung of ox, 463 mediastinal, of lung of horse, 456 of ox, 463 of liver of dog, 432 of horse, 374 of pig, 421 of lungs of dog, 468 of horse, 456 of ox, 462, 463 of pig, 466 of mammary glands, 516 of prostate of horse, 493 of thymus gland of horse, 458 of thyroid gland of dog, 468 of horse, 457 precardiac, of lung of horse, 463 pyriform, 668 of dog, 728

Lobular bronchioles, 457

Lobulation of lungs, 456 of ox, 463 of sheep, 464

Lobules of epididymis, 487 of kidney of horse, 473 of liver of pig, 422 of lung of horse, 457 of mammary glands, 516 of prostate of horse, 493 of testicles of horse, 486 of thymus gland, 458 of thyroid gland, 458

Lobus piriformis, 672

Locus perforatus posticus, 664

Loins of dog, muscles of, 325 of horse, fasciæ of, 235 muscles of, 235 of ox, muscles of, 300 of pig, muscles of, 313

Long ligament of hock joint, 201 muscles, 211

Longissimus capitis et atlantis muscle of horse, 229 muscle of dog, 325 of horse, 237 of ox, 300

Longitudinal bands of cæcum of horse, 364 fissure of cerebrum, 667 of brain, 654 grooves of heart, 528 sinus, superior, 591

Longus capitis muscle, 227 colli muscle of dog, 324 of horse, 228 of pig, 312

Lower, tubercle of, 530

Lumbar arteries, 571, 573 of ox, 618 of pig, 629 enlargement of horse, 648 ganglia, 713

Lumbar lymph glands, 604 of dog, 643 of ox, 625 of pig, 631 nerves of horse, 702 veins, 596, 597 vertebræ, 24 of dog, 151 of horse, 38 of ox, 112 of pig, 138

Lumbo-dorsal fascia, 235

Lumbo-sacral plexus of dog, 731 of horse, 705 of ox, 719 of pig, 723

Lumbricales muscles of dog, 324, 329 of horse, 273, 295 of ox, 305 of pig, 316

Lung, fœtal, of horse, 454 of dog, 468 lobes of, 468 of horse, 453 air-cells of, 457 alveolar ducts of, 457 alveoli of, 457 apex of, 456 basal border of, 456 base of, 456 bronchial branches of, 456 cardiac impression of, 454 notch of, 456 color of, 454 costal surface of, 454 dorsal border of, 455 form of, 454 hilus of, 454 interlobular tissue of, 457 ligament of, 451 lobes of, 456 lobulation of, 456 lobule of, 457 lymph vessels of, 456, 457 mediastinal lobe of, 456 surface of, 454 precardiac lobe of, 463 root of, 456 ventral border of, 454 vessels and nerves of, 457 of ox, 462 apical lobe of, 462, 463 cardiac lobe of, 463 diaphragmatic lobe, 463 fissures of, 462 lobes of, 462, 463 lobulation of, 463 mediastinal lobe of, 463 of pig, 466 lobes of, 466 of sheep, lobulation of, 464

Luys’s body, 665

Lymph, 599, 600 follicles, 600 of small intestine, 363 glands, 599 anal, 605 of pig, 632 atlantal of ox, 623 auricular, of dog, 643 axillary, 605 of dog, 643

Lymph glands, axillary, of ox, 625 of pig, 631 bronchial, 603 of horse, 457 of ox, 624 of pig, 631 cæcal, of pig, 632 cervical, 601 of dog, 643 of ox, 624 of pig, 631 colic, of pig, 632 cubital, of dog, 643 gastric, 604 of pig, 632 hepatic, 605 of pig, 632 iliac, 604 of dog, 643 of ox, 625 of pig, 631 inguinal, 604 of pig, 632 intercostal, 603 ischiatic, 604 of pig, 632 lumbar, 604 of dog, 643 of ox, 625 of pig, 631 mediastinal, 603 of dog, 643 mesenteric, 605 of dog, 643 of pig, 632 of cæcum, 605 of colon, 605 of dog, 643 of Fallopian tubes, 511 of mammary glands of cow, 521 of mare, 517 of ovaries of mare, 510 of ox, 623 of penis, 496 of pig, 630 of prepuce, 497 of spermatic cord, 489 of uterus, 513 of vagina, 514 orbital, 606 pancreatic, 605 parotid, of dog, 643 of pig, 630 pectoral, 601 pharyngeal, 602 of dog, 643 of ox, 623 of pig, 630 popliteal, 606 of dog, 643 of pig, 632 precrural, 606 of pig, 632 prepectoral, of pig, 631 prescapular, 602 of dog, 643 of ox, 624 of pig, 631 renal, of ox, 625 sacral, 604 splenic, 605 of pig, 632

Lymph glands, sternal, of ox, 624 subiliac, 606 submaxillary, 601 of dog, 643 of ox, 623 of pig, 630 subparotid, of ox, 623 thoracic, of pig, 631 nodes, 599. See Lymph glands. nodules, 600 of spleen of horse, 379 spaces, 600

Lymphatic duct, right, 601 system, 599

Lymphocytes, 599, 600

Lymph vessels, 524, 599 of adrenal bodies, 478 of dog, 643 of heart, 535 of kidneys of horse, 475 of lungs of horse, 456, 457 of ox, 623 of pig, 630

Lyssa of dog, 424

Macroscopic anatomy, 17

Maculæ acusticæ, 760

Malar artery, 555 bone of dog, 158 of horse, 67 of ox, 121 of pig, 143

Malaris muscle of horse, 218 of ox, 296

Malleolus, external, of tibia, 103 internal, of tibia, 103

Malleus, 754

Malpighian corpuscles, 379 of kidney, 473, 474 pyramids of kidney, 473

Mammary artery, 580 of ox, 619 glands of bitch, 523 teats of, 523 of cow, 519 of mare, 516 of sow, 522 lymph glands, 604 vein of ox, 622

Mammillary body, 653, 665 of dog, 726 processes, 25, 43

Mandible of dog, 158 of horse, 63 of ox, 122 of pig, 143

Mandibular canal, 64 foramen, 64 nerve of dog, 728 of horse, 681 of ox, 717 of pig, 722 teeth of horse, 344

Mane, 764

Mantle, brain, 668

Manubrium mallei, 754 sterni, 26 of horse, 46

Manus, bones of, 28 of horse, fasciæ of, 262

Manus of horse, muscles of, 262

Marginal cartilage, 171 fissure of horse, 669 of ox, 716 of pig, 721 pole, 716

Margo ciliaris, 744 pupillaris, 744

Marrow of bone, 21

Masseter muscle of dog, 318 of horse, 219 of ox, 297

Masseteric artery, inferior, 547 of ox, 612 fossa of mandible of dog, 159 nerve of horse, 681 vein, 588

Mastication, muscles of, of dog, 318 of horse, 219 of ox, 297 of pig, 311

Mastoid artery, 545 process of horse, 67

Mastoido-humeralis muscle of dog, 320 of horse, 225, 252 of ox, 302 of pig, 314

Matrix of horn, 776 of hoof, 769

Maxilla of dog, 157 of horse, 58 inferior, 63 of ox, 120 of pig, 142

Maxillary artery, external, 547 internal, 551, 612 of dog, 635 of ox, 611 of pig, 627 foramen of horse, 58, 64, 67 nerve of dog, 728 of horse, 679 of pig, 722 process of dog, 158 region of horse, 68 sinus, inferior, of horse, 73 of dog, 161 of horse, 72 of ox, 126 of pig, 146 superior, of horse, 73 teeth of horse, 343 tuberosity of horse, 58 vein, 588 internal, 587 of dog, 642

Maxillo-muscular artery, 547 vein, 588

Maxillo-turbinal bone, 62

Meatus, auditory, external, 56, 748, 759 internal, of horse, 56 common, of nasal cavity, 440 ethmoidal, of nasal cavity, 440 inferior, of nasal cavity of dog, 467 of horse, 439 of pig, 465 of nose of horse, 72

Meatus, middle, of nasal cavity of dog, 467 of horse, 438 of pig, 465 of nose of horse, 72, 71 common, 62 inferior, 62 middle, 62 superior, 62 superior, of nasal cavity of horse, 438 of pig, 465 of nose of horse, 72

Median artery, 559 of ox, 612 nerve, 696 of dog, 731 of horse, 699 of ox, 719 of pig, 723 palatine suture, 69

Mediastinal lobe of lung of horse, 456 of ox, 463 lymph glands, 603 of dog, 643 of ox, 624 pleura of horse, 451

Mediastinum of horse, 450 testis of horse, 486

Medulla oblongata of dog, 735 of horse, 655 of ox, 715 of pig, 720 of thymus gland, 458

Medullary artery, 21 canal of metacarpus of ox, 130 cavity, 19, 20 substance of adrenal bodies, 478 of kidney, 473 velum, 660, 663

Meissner, plexus of, 714

Membrane, atlanto-occipital, inferior, of horse, 176 superior, of horse, 176 basilaris, 760 bones, 22 crico-thyroid, of horse, 444 crico-tracheal, of horse, 445 elastic, of trachea, 449 interosseous, of tibio-fibular articulation, 199 obturator, of horse, 191 œsophageal, of horse, 360 of Descemet, 742 of larynx of horse, 444 of Reissner, 760 synovial, 211 bursal, 211 of anterior digital extensor muscle, 265 of carpal joints, 183 of elbow joint, 181 of hip joint, 193 of lateral digital extensor muscle, 265 vaginal, 211

Membrani nictitans, 736 tympani, 753 secundaria, 753 vestibularis, 760

Membranous labyrinth, 759

Meningeal artery, anterior, 546 middle, 552 of dog, 634 posterior, 545 veins, 592

Meninges, 645

Meniscus, 171

Mental artery, 552 foramen, 63

Mentalis muscle, 216

Mentum of horse, 331

Meridians of eye, 740

Mesaticephalic breed of dogs, 159

Mesencephalon, 663

Mesenteric artery, great, 570 of dog, 638 of ox, 615 of pig, 628, 629 posterior, of ox, 618 small, 571 ganglia, 714 lymph glands, 605 of dog, 643 of ox, 626 of pig, 632 plexus, 714 vein, 597

Mesentery, colic, 354, 369 great, 354, 362

Mesethmoid of ethmoid of horse, 52

Mesocolon of dog, 432

Mesoduodenum, 361

Mesogastric zone of horse, 353

Mesorchium, 489, 490

Mesorectum, 355, 370

Mesosalpinx of bitch, 522 of mare, 511

Mesosternum, 26

Mesotendon, 212

Mesovarium of mare, 509

Metacarpal artery, dorsal, 562 external volar, 562 internal volar, 562 large, 563 of dog, 635, 636, 637 of ox, 614 of pig, 629 palmar, 563 bones, 28 large, 87 of ox, 130 small, of horse, 88 of ox, 130 muscles of horse, 273 of ox, 305 nerves of dog, 731 of horse, 701 tuberosity of horse, 88 vein, 595 of dog, 642 of ox, 621

Metacarpo-phalangeal joints of dog, 208 of horse, 185 of ox, 206 of pig, 208

Metacarpus, 28 of dog, 164 of horse, 87 development of, 88 fascia of, 263

Metacarpus of ox, 128 of pig, 147

Metasternum, 26

Metatarsal arteries, 581 dorsal, 585 of ox, 620 internal superficial plantar, of ox, 619 great, 585 of dog, 640, 641 of pig, 630 bones, 30 of horse, 110, 111 of ox, 135 fascia of horse, 274 nerves of dog, 732 veins, 599 of dog, 643 of ox, 622

Metatarsus of dog, 168 of horse, 110 muscles of, 295 of ox, 135 of pig, 149

Meynert’s commissure, 666

Microscopic anatomy, 17

Mid-brain, 663

Middle cornua of horse, 65 ear of horse, 752 fossa of skull of horse, 71 gluteus muscle of horse, 277 ligament of bladder, 476 of horse, 356 meatus of nasal cavity of dog, 467 of horse, 438 of pig, 465 of nose of horse, 62, 72 patellar ligament, 195 sesamoidean ligament of horse, 188 ventricle of larynx of horse, 447

Milk cistern of cow, 521 teeth of horse, 346 of cow, 521 vein, 301

Mitral valve of horse, 533

Modiolus, 759

Molar glands of ox, 383

Molars, 338, 342

Monakow’s rubrospinal tract, 652

Morgagni, hydatid of, of Fallopian tubes, 511 of testicles, 485

Morphology, 17

Mouth of dog, 423 of horse, 330 cavity of, 330 floor of, 334 mucous membrane of, 330 of ox, 382 of pig, 410

Movable joints, 170 vertebræ, 24

Movements of joint, 171

Mucous glands of larynx, 448 of trachea of horse, 450 membrane, nasal, of horse, 440 of abomasum of ox, 397 of cæcum of dog, 432 of larynx of horse, 448

Mucous membrane of mammary gland of cow, 521 of mouth of horse, 330 of œsophagus of horse, 352 of omasum of ox, 397 of pharynx of horse, 350 of rectum of horse, 370 of reticulum of ox, 395 of stomach of ox, 397 of rumen of ox, 394, 397 of seminal vesicles, 492 of small intestine, 362 of stomach of dog, 430 of tongue of horse, 335 of trachea of horse, 450 of ureters of horse, 475 of urethra of mare, 516 masculina of horse, 499 of uterus of cow, 518 of mare, 513 of vas deferens, 489 of vulva of mare, 515

Müller, muscle of, 736

Multifidus cervicis muscle, 231 dorsi muscle of horse, 238 muscle of pig, 313

Muscles or muscle, 211 abdominal, of horse, 245 of pig, 313 abductor cruris posterior, of dog, 327 digiti quinti, of dog, 324, 329 hallucis, of dog, 329 pollicis brevis et opponens pollicis, of dog, 324 accelerator urinæ, 499 action of, 212 adductor brevis, 282 digiti quinti, of dog, 324 secundi, of dog, 324 hallucis, of dog, 329 longus, of horse, 282 magnus, of horse, 282 of dog, 328, 329 of horse, 282 of ox, 308 of pig, 316 parvus, of horse, 282 pollicis, of dog, 324 anconeus, of horse, 262 of pig, 315 anterior digital extensor, 263 of leg of horse, 288 of ox, 304, 309 extensor, of phalanges, 264 of thigh of ox, 307 antitragicus, 751 arrectores pilorum, 763 articularis genu, of ox, 307 arytenoideus transversus, of larynx of horse, 446 attachments of, 211, 212 auricular, 749 of ox, 774 azygos uvulæ, of horse, 333 belly of, 212 biceps brachii, of dog, 322 of horse, 259 of pig, 314 femoris, of dog, 326 of horse, 278 of ox, 306

Muscle, biceps femoris, of pig, 316 of ox, 302 bipennate, 212 biventer cervicis, of dog, 325 brachial triceps, of horse, 260 brachialis, of dog, 322 of horse, 260 of pig, 315 brachio-radialis, of dog, 322 buccinator, of dog, 318 of horse, 216 of ox, 295 bulbo-cavernosus, of penis of ox, 503 of urethra of horse, 499 capsularis, of dog, 328 of horse, 258, 286 of ox, 307 of pig, 314, 317 cardiac, 211 cervicalis ascendens, of horse, 227 cervico-auricularis, 750 cervico-scutularis, 749 of dog, 780 of ox, 774 chondro-pharyngeus, 350 ciliary, 743 cleido-cervicalis, of dog, 320 cleido-mastoideus, of dog, 320 of horse, 252 of pig, 314 cleido-occipitalis, of pig, 314 cleido-transversarius, 252 coccygeus, of dog, 325 of horse, 230 ventralis lateralis, 240 common digital extensor, 263 of ox, 304 complexus major, of dog, 325 of dog, 325 of horse, 231 of pig, 312 compressor coccygis, of horse, 238 constrictor vestibuli, of mare, 515 vulvæ, of mare, 515 coraco-brachialis, of dog, 322 of horse, 258 of ox, 302 of pig, 314 coraco-radialis, of horse, 259 corrugator supercilii, 218 cremaster, external, 249, 490 of pig, 313 of testicles of ox, 500 of pig, 504 crico-arytenoideus dorsalis, of larynx of horse, 445 lateralis, of horse, 446 crico-pharyngeus, 350 crico-thyroideus, 445 crural triceps, of horse, 284 crureus, of horse, 286 curvator coccygis, 239 cutaneus maximus, of abdomen of horse, 245 scapulæ et humeri, 255

Muscle, deep digital flexor, 271 of leg of horse, 293 of ox, 305 flexor, of ox, 311 gluteus, of horse, 278 pectoral, of ox, 302 deltoid, of dog, 320 of horse, 255 of ox, 302 of pig, 314 depressor coccygis, 240 labii inferioris, of dog, 318 of horse, 216 of ox, 295 of pig, 311 superioris, of ox, 295 rostri, of pig, 311 diaphragm, of dog, 325 of horse, 243 of ox, 300 of pig, 313 digastric, 213 digastricus, of dog, 319 of horse, 222 of ox, 297 of pig, 311 digital extensor, anterior, of dog, 328 of pig, 317 common, of dog, 322 of pig, 315 lateral, of dog, 322, 328 of pig, 315, 317 of ox, 304, 309 of pig, 315 flexor, deep, of dog, 323, 329 of pig, 316, 317 superficial, of dog, 323, 329 of pig, 316, 317 dilatator naris apicalis, of ox, 296 inferior, of horse, 218 of ox, 296 lateralis, of horse, 217 of ox, 295 of pig, 311 superior, of horse, 218 of ox, 296 transversus, of horse, 217 of pig, 311 pupillæ, 744 erector clitoridis, of mare, 515 penis, of horse, 496 extensor brevis, of ox, 310 carpi obliquus, of dog, 322 of horse, 267 of ox, 304 of pig, 315 of dog, 322 radialis brevis, of dog, 322 longus, of dog, 322 of horse, 263 of ox, 304 of pig, 315 ulnaris, of dog, 323 of horse, 268 digitalis brevis, of dog, 328

Muscle, extensor digitalis brevis, of pig, 317 communis, of horse, 263 lateralis, of horse, 265 of leg of horse, 288 longus, of leg of horse, 288 digiti quinti, of dog, 323 tertii et quarti, of dog, 323 hallucis longus, of dog, 328 of pig, 317 indicis proprius, of pig, 315 metacarpi obliquus, of horse, 267 of digits of dog, 322, 329 of second digit of pig, 315 pedis brevis, of horse, 295 of horse, 264, 288 flat, 211 flexor brachii, of horse, 259 carpi externus, of horse, 268 of pig, 316 internus, of dog, 323 of horse, 267 of pig, 315 medius, of dog, 323 of horse, 268 of pig, 315 digitalis pedis, of dog, 329 digiti quinti, of dog, 324 hallucis brevis, of dog, 329 longus, of dog, 329 pedis perforans, of horse, 292, 293 perforans, of horse, 271 perforatus, of horse, 269 pollicis brevis, of dog, 324 form of, 211 frontalis, of ox, 295 fronto-scutularis, 749 gastrocnemius, of dog, 329 of horse, 290 of ox, 311 of pig, 317 gemellus, of horse, 284 of ox, 308 of pig, 317 genio-glossus, of horse, 338 genio-hyoideus, of ox, 298 genito-hyoideus, 223 guteo-biceps, of horse, 278 gluteus accessorius, 278 medius, of dog, 326 of horse, 277 of ox, 306 of pig, 316 profundus, of dog, 326 of horse, 278 of ox, 306 of pig, 316 superficialis, of dog, 326 of horse, 277 of ox, 306 of pig, 316 gracilis, of dog, 328 of horse, 281 of ox, 308 of pig, 316 head of, 213

Muscle, helicis, 752 Homer’s, 736 humeralis obliquus, 260 hyo-epiglotticus, 445 hyo-glossus, of horse, 338 hyoid, of dog, 319 of horse, 222 of ox, 297 hyoideus transversus, 224 of ox, 298 hyo-pharyngeus, 350 hyo-thyreoideus, 445 iliacus, of dog, 326 of horse, 275 of ox, 306 ilio-costalis cervicis, 227 of horse, 236 of ox, 300 ilio-psoas, of horse, 275 incisivus inferior, 216 of ox, 295 superior, of horse, 216 infraspinatus, of dog, 321 of horse, 256 of ox, 302 of pig, 314 insertion of, 212 intercostal, external, of dog, 325 of horse, 240 of pig, 313 internal, of horse, 242 of pig, 313 internal digital extensor, of ox, 304, 309 flexor, of metacarpus, 267 of thigh of ox, 308 interossei, of dog, 324, 329 of horse, 273, 295 of ox, 305 interscutularis, 749 of dog, 780 of ox, 774 interspinales, of dog, 325 of ox, 300 of pig, 313 intertransversales caudæ, 239 colli, of horse, 328 lumborum, 238, 276 of dog, 324, 325 of ox, 300 of pig, 312, 313 ischio-cavernosus, of clitoris of mare, 515 of penis of horse, 496 of ox, 503 ischio-coccygeus, 238 ischio-femoralis, 283 ischio-urethral, 499 jugulomandibularis, 222 kerato-hyoideus, 223 of ox, 298 kerato-pharyngeus, 350 lateral digital extensor, 265 of leg of horse, 288 of ox, 304, 309 lateralis sterni, of horse, 242 latissimus dorsi, of dog, 320 of horse, 251 of ox, 302 of pig, 314 levator labii superioris proprius, of dog, 318

Muscle, levator labii superioris proprius, of horse, 215 of ox, 295 of pig, 311 nasolabialis, of dog, 318 of horse, 214 of ox, 295 of pig, 311 palati, of horse, 333 palpebræ superioris, 219, 738 rostri, of pig, 311 scapulæ hominis, 254 levatores costarum, of dog, 325 of horse, 240 of ox, 300 of pig, 313 long, 211 longissimus capitis et atlantis, of horse, 229 of dog, 325 of horse, 237 of ox, 300 longus capitis, of horse, 227 colli, of dog, 324 of horse, 228 of pig, 312 lumbricales, of dog, 324, 329 of horse, 273, 295 of ox, 305 of pig, 316 malaris, of horse, 218 of ox, 296 masseter, of dog, 318 of horse, 219 of ox, 297 mastoido-humeralis, of dog, 320 of horse, 225, 252 of ox, 302 of pig, 314 mentalis, of horse, 216 metacarpal, of horse, 273 of ox, 305 middle gluteus, of horse, 277 multifidus cervicis, 231 dorsi, of horse, 238 of pig, 313 mylo-hyoideus, of dog, 319 of horse, 222 of ox, 297 names of, 212 nasal, of dog, 318 nerve-supply of, 213 non-striated, 211 oblique extensor, of metacarpus of horse, 267 great, of abdomen, 246 small, of abdomen, 247 of head of horse, 233 obliquus abdominis externus, of dog, 326 of horse, 246 of ox, 301 of pig, 313 internus, of dog, 326 of horse, 247 of ox, 301 of pig, 313 capitis anterior, 233 posterior, of horse, 233 of pig, 313

Muscle, obliquus oculi inferior, 738 superior, 738 obturator externus, 283 of ox, 308 of pig, 317 internus, of horse, 283 of ox, 308 of pig, 317 occipito-hyoideus, 223 of ox, 298 ocular, of horse, 738 of abdomen of dog, 326 of ox, 301 of anus of horse, 371 of arm of horse, 259 of ox, 302 of pig, 314 of auditory ossicles, 755 of back of dog, 325 of horse, 235 of ox, 300 of pig, 313 of cheeks of horse, 213 of digit of horse, 295 of pig, 315 of dog, 318 of eyelids of horse, 218 of face of dog, 318 of ox, 295 of foot of horse, 287 of ox, 309 of pig, 317 of forearm of horse, 262 extensor division, 263 flexor division, 267 of ox, 304 of pig, 315 of head of horse, 213 of pig, 311 of hip, external, of horse, 276 of ox, 306 of pig, 316 of horse, 213 of larynx of horse, 445 of leg of horse, 287, 288, 290 of ox, 309 of pig, 317 of lips of horse, 213 of loins of dog, 325 of horse, 235 of ox, 300 of pig, 313 of manus of horse, 262 of mastication of dog, 318 of horse, 219 of ox, 297 of pig, 311 of metatarsus of horse, 295 of Müller, 736 of neck of dog, 324 of horse, 224, 229 of ox, 298 of pig, 311 of nostrils of horse, 217 of ox, 295 of pelvic limb of dog, 326 of horse, 274 of ox, 306 of pig, 316 of penis of horse, 496 of pharynx of horse, 348 of pig, 311

Muscle of shoulder girdle of horse, 250 of ox, 302 of pig, 314 joint of horse, 181 of horse, 255 of ox, 302 of pig, 314 of tail of dog, 325 of horse, 238 of ox, 300 of pig, 314 of thigh, anterior, 284 external, of horse, 276 of ox, 306 internal, of horse, 281 of pig, 316 of thoracic limb of dog, 319 of horse, 250 of ox, 302 of pig, 314 of thorax of dog, 325 of horse, 240 of ox, 300 of pig, 313 of tongue of horse, 337 omo-hyoideus, 224, 226 of ox, 298 of pig, 312 omo-transversarius of dog, 319 of ox, 302 of pig, 312, 314 orbicular, 211 orbicularis oculi, 218 of ox, 296 oris of dog, 318 of horse, 213 of ox, 295 of pig, 311 origin of, 212 palato-pharyngeus, 349 palmaris brevis, of dog, 324 longus accessorius, of dog, 323 palpebral, of dog, 318 panniculus carnosus, of dog, 318 of pig, 311 of ox, 295 of pig, 311 paramero-biceps, 278 parieto-auricularis, 750 of dog, 780 of ox, 774 parotido-auricularis, 750 pectineus, of dog, 328 of horse, 282 of ox, 308 of pig, 316 pectoral, anterior superficial, of pig, 314 deep, of dog, 320 of horse, 253 of pig, 314 of horse, 252 posterior deep, of pig, 314 superficial, of dog, 320 of horse, 253 of pig, 314 peroneus brevis, of dog, 328 longus of dog, 328 of pig, 317 of horse, 288

Muscle, peroneus tertius, of dog, 328 of horse, 289 of ox, 310 of pig, 317 plantar, of pig, 317 popliteus, of dog, 329 of horse, 294 of pig, 317 preputial, of ox, 503 pronator quadratus, of dog, 324 teres, of dog, 323 of horse, 268 of pig, 315 protractor, of prepuce of ox, 503 psoas major, of dog, 326 of horse, 275 of ox, 306 of pig, 316 minor, of dog, 326 of horse, 275 of ox, 306 of pig, 316 pterygoideus externus, 220 internus, of horse, 219 lateralis, of horse, 220 of ox, 297 pterygo-pharyngeus, of horse, 349 pyriformis, of dog, 326 of horse, 284 quadratus femoris, of dog, 328 of horse, 283 of ox, 308 of pig, 317 lumborum, of dog, 326 of horse, 276 of ox, 306 of pig, 316 plantæ, of dog, 329 quadriceps femoris, 284 of ox, 307 of pig, 317 radialis volaris, of dog, 323 rectus abdominis internus, of pig, 313 of dog, 326 of horse, 248 of ox, 301 of pig, 313 capitis anterior major, of dog, 324 of horse, 227 of ox, 300 minor, of horse, 227 of ox, 300 dorsalis major, of horse, 234 minor, of horse, 234 lateralis, of horse, 228 of ox, 300 of pig, 313 posterior major, of horse, 234 minor, of horse, 234 femoris, of dog, 327 of horse, 284 lateralis, of dog, 324 minor, of dog, 324 oculi, 738 parvus, of horse, 286

Muscle, rectus thoracis, of horse, 242 of pig, 313 relations of, 213 retractor ani, of dog, 432 of horse, 371 costæ, of horse, 242 of pig, 313 oculi, 738 of prepuce of ox, 503 penis, of horse, 496 of ox, 503 rhomboideus capitis, of dog, 320 cervicalis, of dog, 320 of horse, 251 of dog, 320 of horse, 251 of ox, 302 of pig, 314 thoracalis, of dog, 320 of horse, 251 ring-like, 211 rotator, 757 sacro-coccygei, of pig, 314 sacro-coccygeus accessorius, of dog, 325 inferior, of horse, 240 lateralis, of horse, 239 of dog, 325 superior, of horse, 238 ventralis lateralis, of horse, 240 sartorius, of dog, 328 of horse, 281 of ox, 308 of pig, 316 scalenus dorsalis, of dog, 324 of ox, 300 of horse, 227 of pig, 312 ventralis, of dog, 324 of ox, 298 of pig, 312 scansorius, of horse, 278 scapulo-humeralis posticus, of horse, 258 scapulo-ulnaris, of horse, 260 scutularis, 749 semimembranosus, of dog, 327 of horse, 280 of ox, 306 of pig, 316 semispinalis capitis, of horse, 231 colli, of horse, 231 semitendinosus, of dog, 327 of horse, 280 of ox, 306 of pig, 316 serratus anterior hominis, of horse, 254 anticus, of dog, 325 of horse, 235 of ox, 300 of pig, 313 cervicis, of horse, 254 magnus, of dog, 320 of horse, 254 of ox, 302 of pig, 314 posticus, of dog, 325 of horse, 236

Muscle, serratus posticus, of ox, 300 thoracis, of horse, 254 ventralis, of horse, 254 shape of, 212 short, 211 skeletal, 211 small posterior straight, of head of horse, 234 soleus, of horse, 292 of ox, 311 of pig, 317 sphincter, 211, 213 ani externus, of horse, 371 internus, of horse, 371 pupillæ, 744 spinalis et semispinalis, of pig, 313 of horse, 233 spinous, transverse, of neck of horse, 231 splenius, of dog, 324 of horse, 229 of ox, 300 of pig, 312 stapedius, 755 sterno-cephalicus, of dog, 324 of neck of horse, 225 of ox, 298 of pig, 312 sterno-mandibularis, 225 sterno-maxillaris, 225 sterno-thyro-hyoideus, of dog, 319 of horse, 224, 226 of ox, 298 of pig, 312 sterno-thyroideus et sterno-hyoideus, of horse, 226 straight, of head of pig, 312 striated, 211 structure of, 212 stylo-glossus, of horse, 337 stylo-hyoideus, of dog, 319 of horse, 223 of ox, 297 stylo-mandibularis, 222 of ox, 297 stylo-maxillaris, 222 stylo-pharyngeus, 349 sublumbar, of horse, 274 of ox, 306 of pig, 316 subscapularis, of dog, 321 of horse, 257 of ox, 302 of pig, 314 subscapulo-hyoideus, 226 superficial digital flexor, 269 of leg of horse, 292 of ox, 305 flexor, of ox, 311 gluteus, of horse, 277 pectoral, of ox, 302 supinator, of dog, 323 of pig, 315 supraspinatus, of dog, 321 of horse, 256 of ox, 302 of pig, 314 tarsal, 736 temporalis, of dog, 318

Muscle, temporalis, of horse, 219 of ox, 297 tendo femorotarseus, 289 tensor fasciæ antibrachii, of dog, 322 of horse, 260 of ox, 303 of pig, 315 latæ, of dog, 326 of horse, 276 of ox, 306 of pig, 316 palati, of horse, 333 tympani, 755 teres major, of dog, 322 of horse, 258 of ox, 302 of pig, 314 minor, of dog, 321 of horse, 256 of ox, 302 of pig, 314 thyro-arytenoideus, 446 thyro-hyoideus, 445 thyro-pharyngeus, 350 tibialis anterior, of dog, 328 of horse, 290 of ox, 310 of pig, 317 posterior, of dog, 329 trachelo-mastoideus, of dog, 325 of horse, 229 of pig, 312 tragicus, 751 transversalis costarum, of dog, 325 of horse, 236 of ox, 300 of pig, 313 transversus abdominis, of dog, 326 of horse, 248 of ox, 302 of pig, 313 costarum, of horse, 242 thoracis, of horse, 242 of pig, 313 trapezius cervicalis, of horse, 250 of dog, 319 of horse, 250 of ox, 302 of pig, 314 thoracalis of horse, 251 triangularis sterni, 242 triceps brachii, of horse, 260 of dog, 322 of ox, 303 of pig, 315 suræ, of horse, 292 ulnaris lateralis, of dog, 323 medialis, of dog, 323 unipennate, 212 unstriped, 211 urethral, of dog, 507 of horse, 499 of mare, 516 of ox, 504 of pig, 506 vastus externus, of horse, 285 intermedius, of horse, 286 of ox, 307

Muscle, vastus internus, of horse, 286 ventricularis et vocalis, 446 vocalis, of horse, 446 volar, of pig, 315 Wilson’s, of dog, 509 of ox, 504 zygomatico-auricularis, 749 of ox, 774 zygomaticus, of dog, 318 of horse, 215 of ox, 295 of pig, 311

Muscular bands of great colon of horse, 368 coat of œsophagus, 352 layer of trachea of horse, 450 process of arytenoid cartilages of larynx, 443 of temporal bone, 57 ring of cæcum of horse, 365 system, 211

Muscularis mucosæ of small intestine, 362

Musculi papillares of left ventricle, 533 of right ventricle, 531 pectinati, in right atrium, 530

Musculo-cutaneous nerves, 696 of dog, 730 of horse, 697 of leg of horse, 708

Musculo-spiral groove, 77 nerve of horse, 698

Myenteric plexus, 714

Mylo-hyoid nerve, 682 of dog, 728

Mylo-hyoideus muscle of dog, 319 of horse, 222 of ox, 297

Myocardium, 534

Myology, 211

Nares, anterior, of horse, 436 posterior, of horse, 68, 348, 440

Nasal artery, 550 of ox, 611 bones of dog, 158 of horse, 61 of ox, 121 of pig, 143 cavity of dog, 161, 466, 467 of horse, 71, 436 common meatus of, 440 ethmoidal meatuses, 440 inferior meatus of, 439 middle meatus of, 438 parietal cartilage, 437 superior meatus of, 438 vessels and nerves, 437 of ox, 125, 458 of pig, 145, 464 structure of, 436 crest of horse, 71 glands of horse, 440 mucous membrane, 440 muscles of dog, 318 nerve of dog, 728 of horse, 679

Nasal process of horse, 60 region of horse, 66 septum, 71, 72, 73, 437 vein of ox, 621 of pig, 630

Naso-ciliary nerve, 678 of ox, 717 of pig, 722

Nasofrontal suture, 55, 61 of ox, 119

Naso-labial glands of ox, 775

Naso-lacrimal duct of horse, 436, 737 canal for, 71 groove for, 71 of dog, 779 of ox, 773 suture of horse, 61

Naso-maxillary fissure, 73, 439 notch of horse, 61 suture of horse, 61

Naso-palatine canal of ox, 384

Naso-turbinal bones, 62

Navicular bone, 92, 111 bursa of deep digital flexor muscle, 272 ligaments, inferior, 190 suspensory, of horse, 189

Neck of dog, muscles of, 324 of horse, fascia of, 224 fascia propria of, 224 muscles of, 224, 229 panniculus carnosus, 224 transverse spinous muscle of, 231 of ox, muscles of, 298 of pig, muscles of, 311 of tooth, 339

Nerve or nerves, abducent, 683 alveolar, 681, 682 of dog, 729 auditory, 686 auricular, 685 posterior, 695 auriculo-palpebral, 685 of dog, 729 of ox, 717 axillary, 697 of horse, 697 buccal, 685 of dog, 729 of ox, 717 of pig, 722 buccinator, of horse, 681 cardiac, 712 cervical, of horse, 694 chorda tympani, 683, 684 ciliary, of dog, 728 of horse, 679 circumflex, of horse, 697 classification of, 644 coccygeal, of horse, 710 cochlea, 686 cranial, of dog, 728 of horse, 676 of ox, 717 of pig, 722 crural, anterior, 706 cutaneous, of leg, 708 of neck, 695 dental, 681, 682 depressor, of dog, 730 digastric, 685 digital, of dog, 730, 732

Nerve, digital, of horse, 701 of ox, 718 of pig, 723 eighth, 686 eleventh, 690 ethmoidal, 678 of dog, 728 facial, 684 of dog, 729 of ox, 717 femoral, of horse, 706 fifth, of horse, 677 first, of horse, 676 fourth, of horse, 677 frontal, of dog, 728 of horse, 678 of ox, 717 glosso-pharyngeal, 686 gluteal, of horse, 706 hemorrhoidal, of horse, 710 hypoglossal, 692 of dog, 730 of ox, 717 of pig, 722 ilio-hypogastric, 704 ilio-inguinal, of horse, 704 infraorbital, of dog, 728 of horse, 681 of pig, 722 infratrochlear, 679 of dog, 728 intercostal, of horse, 702 labial, of horse, 681 lacrimal, of dog, 728 of horse, 678 of ox, 717 of pig, 722 laryngeal, of dog, 729 recurrent, 689 superior, 689 lingual, 683 of dog, 729 lumbar, of horse, 702 mandibular, of dog, 728 of horse, 681 of ox, 717 of pig, 722 masseteric, of horse, 681 maxillary, of dog, 728 of horse, 679 of pig, 722 median, 696 of dog, 731 of horse, 699 of ox, 719 of pig, 723 metacarpal, of dog, 731 of horse, 701 metatarsal, of dog, 732 musculo-cutaneous, 696 of dog, 730 of horse, 697, 698 of leg of horse, 708 musculo-spiral, of horse, 698 mylo-hyoid, 682 of dog, 728 nasal, of dog, 728 of horse, 697, 681 naso-ciliary, 678 of ox, 717 of pig, 722 ninth, 686 oculomotor, of horse, 677 of ox, 717

Nerve, obturator, of horse, 706 œsophageal, of dog, 729 of adrenal bodies, 478 of articulations, 171 of bladder of horse, 477 of cornea, 742 of external ear, 752 of eye, 737 of Fallopian tubes, 511 of hoof, 771 of mammary glands of cow, 521 of mare, 517 of ovaries of mare, 510 of penis of horse, 496 of prepuce of horse, 497 of pterygoid canal, 681 of skin, 762 of spermatic cord, 489 of tympanum, 755 of uterus of mare, 513 of vagina of mare, 514 of vascular tunic of eye, 745 of veins, 525 olfactory, of horse, 676 ophthalmic, 678 of dog, 728 optic, of horse, 676 palatine, of dog, 728 of horse, 679, 680 pectoral, 696 peroneal, deep, of ox, 720 of dog, 732 of horse, 708 of pig, 723 petrosal, 684 pharyngeal, of dog, 729 phrenic, 695 plantar, of dog, 732 of horse, 709 of ox, 720 of pig, 723 pneumogastric, 687 pterygoid, of horse, 681 pudic, of horse, 710 pulmonary, of horse, 457 radial, of dog, 730 of horse, 696, 698 of ox, 718 sacral, of horse, 710 saphenous, external, of horse, 708 of dog, 731 of horse, 706 sciatic, of horse, 707 second, of horse, 676 seventh, 684 sixth, 683 spermatic, external, 704 sphenopalatine, of dog, 728 of horse, 679 spinal accessory, 690 of ox, 717 of dog, 730 of horse, 692 of ox, 717 of pig, 723 splanchnic, 713 stapedial, 684 subscapular, 696 supply of eye muscles, 739 suprascapular, 696 of horse, 697 temporal, 682

Nerve, temporal, of dog, 728 of horse, 681 of ox, 717 of pig, 722 tenth, 687 third, of horse, 677 thoracic, anterior, 696 of horse, 697, 702 thoraco-dorsal, 697 tibial, anterior, 708 of dog, 732 of horse, 708 of ox, 720 trifacial, of horse, 677 trigeminal, of horse, 677 trochlear, of horse, 677 twelfth, 692 tympanic, 686 ulnar, of dog, 730 of horse, 696, 698 of ox, 718 of pig, 723 vagus, 687 of dog, 729 of ox, 717 of pig, 722 ventral, of dog, 729 vestibular, 686, 761 Vidian, 681 volar, of horse, 701 of ox, 718, 719 zygomatic, of dog, 728 of horse, 679

Nerve-cells, 644

Nerve-plexus, 645

Nervous system, 644 of dog, 724 of horse, 724 of ox, 715 of pig, 720 symphathetic, 710

Nervus accessorius, 690 lacrimalis, 678 oculomotorius, of horse, 677 olfactorius of horse, 676 ophthalmicus, 678 opticus of horse, 676 trigeminus, 677 trochlearis, 677

Neuroglia, 644

Neurology, 644

Neurone, 644

Ninth nerve, 686

Nippers, 339

Nipple of mammary gland of mare, 516

Nodules, lymph, 600 of spleen of horse, 379

Nodulus, 660

Nose of horse, common meatus of, 62 inferior meatus of, 62, 72 meatuses of, 71 middle meatus of, 62, 72 superior meatus of, 62, 72

Nostrils of dog, 466 of horse, 436 of ox, 458 of pig, 464

Notch, acetabular, of horse, 96 cardiac, of lungs, 456 carotid, of horse, 51 glenoid, of horse, 76 naso-maxillary, of horse, 61

Notch, œsophageal, of dog, 434 of tibia of horse, 102 oval, of horse, 51 popliteal, of tibia, 102 sciatic, lesser, of horse, 95 semilunar, of ulna, 82 sigmoid, of horse, 64 sphenoidal, of horse, 55 spinous, of horse, 51

Nuchal surface of skull of dog, 160 of horse, 69 of ox, 124 of pig, 145

Nuclei of origin of nerves, 644

Nucleocerebellar fasciculus, 661

Nucleus alæ cinereæ, 690 amygdalæ, 676 caudatus, 675 cuneatus, 658 dorsal sensory, 690 dorsalis, 651 facial, 684 gracilis, 658 hypoglossal, 692 hypothalamicus, 665 lenticular, 675 lentiformis, 675 lentis, 747 of solitary tract, 690 olivaris caudatis, 658 nasalis, 660 ruber, 665 subthalamic, 665

Nutrient artery, 21 of femur, 580 of humerus, 559 of tibia, 581 foramen of femur, 97 of humerus, 78 of ilium, 94 of metacarpus, 88 of tibia, 100

Obex, 663

Oblique extensor muscle of metacarpus of horse, 267 muscle, small, of head of horse, 233

Obliquus abdominis externus muscle of dog, 326 of horse, 246 of ox, 301 of pig, 313 internus muscle of dog, 326 of horse, 247 of ox, 301 of pig, 313 capitis anterior muscle of horse, 233 posterior muscle of horse, 233 of pig, 313 oculi inferior, 738 superior, 738

Obturator artery, 577 of ox, 619 externus muscle of horse, 283 of ox, 308

Obturator externus muscle of pig, 317 foramen of dog, 167 of horse, 96, 97 of ox, 132 internus muscle of horse, 283 of ox, 308 of pig, 317 membrane of horse, 191 nerves of horse, 706 vein, 598

Occipital artery, 544 of dog, 633 of ox, 611 of pig, 627 bone of dog, 154 of horse, 47 development, 50 of ox, 115 of pig, 139 condyles of horse, 48, 68, 69 crest of horse, 50, 69 protuberance, external, 50 internal, 54 sinus, 591 vein, 588

Occipito-hyoideus muscle, 223 of ox, 298

Ocular muscles of horse, 738 sheath of horse, 738

Oculomotor nerve of horse, 677 of ox, 717

Odontoid ligament, 176 process of axis of horse, 34 of ox, 112

Œdema glottidis of horse, 448

Œsophageal artery, 565, 567 of ox, 614 of pig, 627 groove of ox, 394 of sheep, 408 nerve of dog, 729 notch of dog, 434 opening of horse, 348 plexus, 713 of dog, 730 vein, 587

Œsophagus of dog, 428 of horse, 350 of ox, 389 of pig, 417 of sheep, 407

Olecranon fossa, 80 of horse, 83

Olfactory bulb, 653, 671 of dog, 727 of ox, 717 of pig, 721 cells, 772 fossa of horse, 52, 70 glands of horse, 440, 772 nerve of horse, 676 organs of dog, 781 of pig, 779 peduncle, 671 striæ, 671 tracts, 671 of pig, 721

Olivary eminence of dog, 725 nucleus, anterior, 660 posterior, 658

Olivocerebellar fibers, 661

Omaso-abomasal artery of ox, 615

Omaso-abomasal orifice of ox, 396

Omasum of ox, 390, 392 of sheep, 408

Omental cavity of horse, 380

Omentum, gastro-colic, 358 gastro-hepatic, 354, 358 gastro-splenic, 354, 358, 379 great, of horse, 354, 358 of ox, 396 lesser, of ox, 396

Omo-hyoideus muscle, 224, 226 of ox, 298 of pig, 312

Omo-transversarius muscle of dog, 319 of ox, 302 of pig, 312, 314

Ophthalmic artery, 553 of dog, 635 of ox, 612 nerve, 678 of dog, 728 vein, 590

Optic axis, 740 chiasm, 666 commissure, 666 foramen, 50, 51, 67, 70 groove of horse, 50 nerve of horse, 676 papilla, 745 of ox, 774 of pig, 778 recess, 667 thalamus, 664 tract, 664, 666 of ox, 716

Ora serrata, 745

Orbicular muscles, 211

Orbicularis oculi muscle, 218 of ox, 296 oris muscle of dog, 318 of horse, 213 of ox, 295 of pig, 311

Orbit of horse, 67

Orbital artery, 555 ducts of dog, 427 fascia of horse, 738 fissure of horse, 51 foramen, internal, 67, 70 gland of dog, 427 region of horse, 67 veins of ox, 621 wings of horse, 51

Organ of Corti, 760 of Jacobson, 772 of sense, 734 vomero-nasal, of horse, 440

Orifice, aortic, of heart, 533 atrio-ventricular, left, of ventricle, 530, 533 right, of ventricle, 530, 531 cæco-colic, of horse, 364 fronto-maxillary, 73 ileo-cæcal, of horse, 364 laryngeal, of horse, 348 of anterior vena cava of horse, 529 of coronary sinus, 529 of posterior vena cava, 529 omaso-abomasal, of ox, 396 preputial, of horse, 496

Orifice, pulmonary, of right ventricle, 531 reticulo-omasal, of ox, 394 rumino-reticular, of ox, 393 ureteral, of horse, 477 urethral, external, of cow, 519 of horse, 499 of mare, 515 of ox, 503 internal, of horse, 477 of male horse, 499 of pig, 505

Os coronæ of horse, 89 coxæ, 29 of horse, 92 of pig, 148 pedis of dog, 506 of horse, 90 rostri of pig, 143, 464 suffraginis of horse, 89 uteri externum of mare, 513 internum of mare, 513

Ossa cordis of ox, 609

Osseous labyrinth, 758

Ossicles, auditory, 754

Ossification, 22 endochondral, 22 intramembranous, 22 of vertebræ, 25

Osteoblasts, 22

Osteoclasts, 22

Osteogenesis, 22

Osteology, 19

Ostium abdominale of mare, 511 uterinum of mare, 511

Otic ganglion, 681, 711 of ox, 717

Outlet of pelvis, 97, 354

Ova of mare, 510

Oval notch of horse, 51

Ovarian artery, 571 of mare, 510 ligament of bitch, 522 of mare, 509

Ovaries of bitch, 522 of cow, 517 of mare, 508 of sow, 521

Overextended joints, 171

Overshot dog, 425

Ovulation fossa of mare, 509 in mare, 510

Pacchionian bodies, 647

Pad, dental, of ox, 384

Pads of dog, 780

Palate, hard, of dog, 423 of horse, 69, 332 of ox, 383 of pig, 411 of sheep, 405 soft, of dog, 424 of horse, 332 of ox, 384 of pig, 411

Palatine artery, 555 of pig, 627 bones of horse, 60 of ox, 120 of pig, 142 canal of horse, 58

Palatine cleft of horse, 60, 69, 71 foramen, posterior, 58, 68 glands of horse, 333 groove of horse, 59, 69 nerve of dog, 728 of horse, 679, 680 process of dog, 157 of maxillæ of horse, 58 of premaxillæ of horse, 60 region of horse, 68 sinus of ox, 120, 126 suture, median, 69 transverse, of horse, 69 vein, 589

Palato-labial artery, 555

Palato-pharyngeus muscle, 349

Pallium, 668

Palmar metacarpal artery, 563

Palmaris brevis muscle of dog, 324 longus accessorius muscle of dog, 323

Palpebral fissure of horse, 735 ligament, 736 muscle of dog, 318 sebum, 736

Pampiniform plexus of testicles of horse, 487

Pancreas aselli of dog, 643 of dog, 434 of horse, 371 of ox, 404 of pig, 423 of sheep, 410

Pancreatic arteries, 569 duct, accessory, of dog, 431 of horse, 373 of dog, 431, 434 of horse, 372 of ox, 398 of pig, 419, 423 lymph glands, 605 vein, 597

Pancreatico-duodenal artery, 569

Panniculus, abdominal, 245 adiposus of horse, 761 carnosus of dog, 318 of head of horse, 213 of horse, 213, 761 of neck of horse, 224 of pig, 311 facial, of pig, 311 muscle of ox, 295 scapulo-humeral portion, 255 thoracic portion, 255

Papilla communis of kidney, 474 filiform, of tongue, 336 foliate, of tongue, 336 fungiform, of tongue, 336 hair, 763 of cheeks of ox, 382 of skin, 762 of tongue, 336 optic, 745 of ox, 774 renalis of ox, 480 vallate, of tongue, 336

Paramastoid process, 48, 68, 69

Paramero-biceps muscle, 278

Paranasal sinuses of horse, 72

Parapharyngeal lymph gland of ox, 623

Parathyroid gland of dog, 468 of horse, 458 of ox, 464

Parenchyma of adrenal bodies, 478 of liver, 377 of mammary glands, 516 testis, 486

Parietal bones of dog, 155 of horse, 54 of ox, 117 of pig, 140 cartilage of nasal cavity, 437 crest of ox, 117 pleura of horse, 451 region of skull of horse, 66

Parieto-auricularis, 750 of dog, 780 of ox, 774

Parieto-frontal suture, 54, 55

Parieto-occipital suture, 54

Parieto-temporal canal, 54, 57 suture, 56

Parolfactory area, 671

Parotid artery, 543 of pig, 627 duct of dog, 423, 427 of horse, 347 of pig, 411, 414 gland of dog, 427 of horse, 346 of ox, 388 of pig, 414 lymph gland of dog, 643 of pig, 630

Parotido-auricularis, 750 of dog, 780 of ox, 774

Pars basilaris pontis, 660 ciliaris retinæ, 745 dorsalis pontis, 660 intercartilaginea of larynx, 448 intermembranacea of larynx, 448 iridica retinæ, 745 optica retinæ, 745

Pastern bone, 89 joint, 188 movements of, 189

Patches, Peyer’s, of horse, 363 of ox, 398 of pig, 419

Patella, 29 of dog, 168 of horse, 104 of ox, 134 of pig, 149

Patellar ligaments, 195, 196

Pathetic foramen, 67

Pectineus muscle of dog, 328 of horse, 282 of ox, 307 of pig, 316

Pectoral fascia of horse, 252 lymph glands, 602 muscle, anterior superficial, of pig, 314 deep, of dog, 320 of horse, 253, 254 of ox, 302 of pig, 314

Pectoral muscle, deep, posterior, of pig, 314 of horse, 252 posterior superficial, of pig, 314 superficial, of dog, 320 of horse, 253 of ox, 302 nerve, 696

Peduncles, cerebellar, 661 cerebral, 664 of ox, 716 of pig, 720 middle cerebellar, 659 olfactory, 671

Pelvic artery of horse, 97, 354 of ox, 133, 390 fascia of horse, 273 flexure of horse, 366 girdle, 29 of horse, 92 limb, bones of, 29 of dog, articulations of, 209 bones of, 165 muscles of, 326 of horse, articulations of, 190 bones of, 92 fasciæ of, 273 muscles of, 274 of ox, articulations of, 209 bones of, 131 muscles of, 306 of pig, articulations of, 209 bones of, 148 muscles of, 316 peritoneum of horse, 355 plexus, 713, 715

Pelvis of dog, 167 inlet of, 167 of horse, 96 axis of, 97 conjugate diameter, 97 inlet of, 96 outlet of, 97 sacro-pubic diameter, 97 sexual differences of, 97 transverse diameter, 97 of kidney of horse, 473 of ox, 132 axis of, 133 conjugate diameter, 132 inlet of, 132 of pig, 148 inlet of, 148

Penis, glans, of dog, 506 of horse, 495 of ox, 503 of dog, 506 glans, 506 os of, 506 prepuce of, 507 of horse, 494 arteries of, 496 body of, 494 corona glandis of, 495 corpus cavernosum, 495 spongiosum, 495 fossa glandis of, 495 glans, 495

Penis of horse, ischio-cavernosus muscle of, 496 lymphatics of, 496 muscles of, 496 nerves of, 496 root of, 494 sheath of, 496 structure of, 495 suspensory ligaments, 494 veins of, 496 vessels and nerves, 496 of ox, 503 bulbo-cavernosus muscle of, 503 glans, 503 ischio-cavernosus muscle of, 503 prepuce of, 503 retractor muscle of, 503 septum of, 503 of pig, 505 prepuce of, 506

Periarticular ligaments, 171

Pericardiac pleura, 452

Pericardium of dog, 632 of horse, 525 of ox, 608 of pig, 626

Perichorioid space, 742

Perineal artery, 574 of dog, 641 vein of ox, 622

Periople, 765 of ox, 775 structure of, 768

Perioplic matrix, 769

Periorbita of horse, 738

Periosteal artery, 21

Periosteum, 21 alveolar, of teeth, 339

Peritoneal ring of horse, 490

Peritoneum of horse, 353, 379 pelvic, 355

Permanent teeth of horse, 340

Peroneal artery, 585 nerve, deep, of ox, 720 of dog, 732 of horse, 708 of pig, 723 superficial, of ox, 719

Peroneus brevis muscle of dog, 328 longus muscle of dog, 328 of pig, 317 muscle of horse, 288 tertius muscle of dog, 328 of horse, 289 of ox, 310 of pig, 317

Perpendicular artery, 564 plate of ethmoid, 52

Petro-basilar canal of temporal bone of dog, 156

Petrosal crest of horse, 57, 70 nerve, 684 sinus, inferior, 592 superior, 591

Petro-tympanic fissure, 57

Petrous ganglion, 686 temporal bone, 56 of ox, 120

Peyer’s patches of horse, 363 of ox, 398

Peyer’s patches of pig, 419

Phacoid bone of cat, 164

Phalanges, 29 distal, 29 first, 29 of dog, 165 of horse, 89, 111 of ox, 130 middle, 29 of dog, 165 of horse, 89, 111 ligaments of lateral cartilages of, 190 of ox, 130, 136 of pig, 148, 150 proximal, 29 second, 29 of dog, 165 of horse, 89, 111 of ox, 130 third, 29 of dog, 165 of horse, 90, 111 of ox, 130

Pharyngeal aperture, 447 aponeurosis, 350 artery, 548 of ox, 611 fascia of horse, 213 isthmus of horse, 350 lymph glands, 602 of dog, 643 of pig, 630 nerve of dog, 729 opening of Eustachian tube, 755 plexus of dog, 729 recess, 350

Pharynx of dog, 427 of horse, 348 of ox, 389 of pig, 416 of sheep, 407

Philosophical anatomy, 17

Philtrum of horse, 331

Phrenic artery, 565 of ox, 614 nerve, 695 vein, 596

Phrenico-abdominal artery of dog, 639 of pig, 628

Pia mater, 647

Pillar, anterior, of soft palate of horse, 333 of fornix, 173 of rumen of ox, 393 posterior, of soft palate, 333, 350

Pilomotor fibers, 711

Pinchers, 339

Pineal body, 665 of ox, 716 recess, 667

Pinna of horse, 747

Pituitary body, 653, 664, 665 of dog, 726 of ox, 716 fossa of horse, 50

Pivot joint, 172

Plantar arch, 581 arteries, 581 of dog, 640 of ox, 619

Plantar cushion, 771 artery of, 564 flexion of joints, 171 fossa of femur, 99 ligament of hock joint, 201 muscles of pig, 317 nerves of dog, 732 of horse, 709 of ox, 720 of pig, 723 venous arch, 599

Planum nuchale of horse, 50 parietale of horse, 50

Plate, dental, of ox, 384

Pleura of horse, 451 costal, 451 diaphragmatic, 451 mediastinal, 451 parietal part, 451 pericardiac, 452 pulmonary, 452 sagittal fold of, 452 visceral, 452 of ox, 461 of thoracic cavity, 450 pericardica of horse, 525

Plexus, abdominal, 713 adrenal, 714 annularis, 742 aortic, 712 basilar, 592 brachial, of dog, 730 of horse, 696 of ox, 717 of pig, 723 cardiac, 712 carotid, 711 cavernous, 711 cervical, 694 chorioid, 666 cœliac, 714 coronary, 595 dorsal, 595 gangliosus ciliaris, 745 gastric, 714 of dog, 729 hepatic, 714 of horse, 377 hypogastric, 715 interosseous, 595 lumbo-sacral, of dog, 731 of horse, 705 of ox, 719 of pig, 723 mesenteric, 714 myenteric, 714 œsophageal, 713 of dog, 730 of Meissner, 714 pampiniform, of testicle, 487 pelvic, 715 pharyngeal, of dog, 729 pulmonary, 690, 712 of dog, 730 renal, 714 solar, 713 spermatic, 487, 714 splenic, 714 submucous, 714 tympanic, 687 utero-ovarian, 714 venosi, 524 venosus scleræ, 741 venous, of urethra, 516

Plexus, volar, 595

Plica iridis, 744 salpingo-pharyngea, 756 venæ cavæ of horse, 452 ventriculares of horse, 447 vocalis of horse, 448

Pneumogastric nerve, 687

Point of hock, 106

Polus lentis, 747

Polymastia of cow, 520

Polythelia of cow, 520

Pons of dog, 725 of horse, 659 of ox, 716 of pig, 720

Popliteal artery, 581 of ox, 619 of pig, 630 line of tibia, 100 lymph glands, 606 of dog, 643 of ox, 626 of pig, 632 nerves, external, 708 notch of tibia, 102 vein, 599 of dog, 642

Popliteus muscle of dog, 329 of horse, 294 of pig, 317

Portal fissure of liver of dog, 434 of horse, 373 of ox, 402 ring of horse, 372 system, 524 vein, 596 of horse, 377 of ox, 623

Portio clavicularis, 253 prescapularis, 253 sternocostalis, 253

Posterior angle of ilium, 94 of pubis, 96 of scapula, 76 annular ligament, 263 clinoid process of dog, 156 of pig, 142 cornu of thyroid cartilage, 442 crucial ligament of horse, 198 deep pectoral muscle of horse, 254 of pig, 314 facets of horse, 441 ligament of pastern joint, 188 of temporo-mandibular articulation, 179 nares of horse, 68, 348, 440 obliquus capitis muscle, 233 palatine foramen, 58, 68 pillar of soft palate, 333, 350 straight muscle, small, of head, 234 superficial pectoral muscle of horse, 253 of pig, 314 tibialis muscle of dog, 329

Postero-external angle of ischium of horse, 95

Post-glenoid fossa, 56 process, 67

Pouch, cutaneous, of sheep, 111 recto-genital, of horse, 356 recto-vesical, of horse, 356 vesico-genital, of horse, 356

Poupart’s ligament, 246

Precrural lymph glands, 606 of ox, 626 of pig, 632

Premaxilla of dog, 157 of horse, 59 of ox, 120 of pig, 142

Premaxillary region, 66

Premolars, 338, 342

Prenasal bone of pig, 143

Preorbital region of horse, 68

Prepectoral lymph glands of ox, 624 of pig, 631

Preplantar artery, 564

Prepubic artery, 579 tendon of horse, 250

Prepuce of clitoris of mare, 515 of dog, 507 of horse, 496 raphé of, 496 structure of, 497 of ox, 503 of pig, 506

Preputial diverticulum of pig, 506 frenum of horse, 497 glands of horse, 497 muscles of ox, 503 orifice of horse, 496 ring of horse, 497

Prescapular lymph glands, 602 of dog, 643 of ox, 624 of pig, 631

Presternum, 26

Presylvian fissure of dog, 727 of horse, 669 of pig, 721

Prevertebral artery, 545

Process, angular, of mandible of dog, 159 auditory, external, of horse, 56, 67 basilar, of horse, 48 of third phalanx, 91 ciliary, 743 clinoid, anterior, of sphenoid bone of dog, 156 posterior, of sphenoid bone of dog, 156 of pig, 142 coracoid, of horse, 77 coronoid of mandible of horse, 64 of radius of horse, 80 frontal, of dog, 157 hyoid, of horse, 57 lacrimal, of dog, 158 lingual, of horse, 65 mammillary, 25 of horse, 43 mastoid, of horse, 67 maxillary, of dog, 158 muscular, of arytenoid cartilages of horse, 443 of temporal bone, 57 nasal, of horse, 60

Process, odontoid, of axis of horse, 34 of ox, 112 of urethra masculina, 498 palatine, of dog, 157 of maxillæ of horse, 58 of premaxillæ, 60 paramastoid, 48, 68, 69 postglenoid, of horse, 67 pterygoid, of horse, 51 retrossal, of horse, 91 spinous, of axis of horse, 34 of ox, 112 of cervical vertebræ of ox, 112 of lumbar vertebræ of horse, 39 of ox, 114 of thoracic vertebræ of horse, 36 of ox, 112 of vertebræ of horse, 42 styloid, of horse, 48, 68, 69 of radius of dog, 161 of temporal bone, 57 of ulna of horse, 82 of ox, 129 supraorbital, of horse, 55, 56 of ox, 119 temporal, of maxillary bone of horse, 58 urethral, of horse, 495 vocal, of horse, 443 zygomatic, of frontal bone, 55 of maxillary bone, 58 of temporal bone, 56

Processus anconæus of horse, 82 cornu of ox, 118 uncinatus of dog, 780 vaginalis of horse, 491

Projection fibers, 676

Prominentia laryngea, 442

Promontory, 753

Pronator quadratus muscle of dog, 324 teres muscle of dog, 323 of horse, 268 of pig, 315

Prostate of dog, 506 of horse, 493 of ox, 502 of pig, 505

Prostatic ducts of horse, 499 of ox, 502 utricle of horse, 493

Protractor muscles of prepuce of ox, 503

Protuberance, occipital, external, 50 internal, 54

Proximal border of hoof, 765 interphalangeal joint, 188 sesamoid bones of horse, 92 of ox, 131

Psoas major muscle of dog, 326 of horse, 275 of ox, 306 of pig, 316 minor muscle of dog, 326 of horse, 275 of ox, 306 of pig, 316

Psoas tubercle of horse, 93

Pterygoid artery, 552 bones of dog, 158 of horse, 60 of ox, 121 of pig, 143 canal of horse, 51, 61 crest of horse, 51 foramen of horse, 51, 68 nerve of horse, 681 processes of horse, 51 veins, 587

Pterygoideus externus muscle of horse, 220 internus muscle of horse, 219 lateralis muscle of horse, 220 muscle of ox, 297

Pterygo-palatine fossa, 60 of horse, 67

Pterygo-pharyngeus muscle of horse, 349

Pubis, 29 of dog, 167 of horse, 95 of ox, 131 of pig, 148

Pubo-femoral ligament of horse, 193, 250

Pudic artery, external, 580 internal, 573 of ox, 619 of pig, 630 nerve of horse, 710 vein, external, 598 of ox, 622

Pulmonary artery, 524, 535 of horse, 457 circulation, 607 nerves of horse, 457 orifice of right ventricle, 531 pleura of horse, 452 plexus, 690, 712 of dog, 730 valve of horse, 532 veins, 524, 585 of horse, 457 openings of, left atrium, 530

Pulp cavity of teeth, 339 of teeth, 339 spleen, of horse, 379

Puncta lacrimalia of horse, 737

Punctum lacrimale in pig, 778 lacrimalis, 736

Pupil, 744 of dog, 779 of pig, 778

Pupillary border of iris, 744

Pyloric artery, 569 glands of stomach, 360 sphincter of horse, 359

Pyramid or pyramids, of Ferrein, 473 of oblongata, 655 renal, of horse, 473 of ox, 480

Pyramidal decussation, 655, 658 fasciculi, 660 tracts, 658 of oblongata, 658

Pyriform lobe, 653, 668, 672 of dog, 728

Pyriformis muscle of dog, 326 of horse, 284 sinus of horse, 350

Quadratus femoris muscle of dog, 328 of horse, 283 of ox, 308 of pig, 317 lumborum muscle of dog, 326 of horse, 276 of ox, 306 of pig, 316 plantæ muscle of dog, 329

Quadriceps femoris muscle of horse, 284 of ox, 307 of pig, 317

Quarters, 764

Radial artery, anterior, 559 of dog, 635 of ox, 613 posterior, 559 of ox, 612 carpal bone, 83 nerve of dog, 730 of horse, 696, 698 of ox, 718 veins, 595 of dog, 642

Radialis volaris muscle of dog, 323

Radiate ligament of horse, 177

Radiatio corporis callosi, 672

Radii lentis, 747

Radio-carpal joint, 183 sac of horse, 183

Radio-ulnar articulation, 182

Radius, 28 of dog, 163 of horse, 80 development of, 82 of ox, 127 of pig, 147