The myology of the pigeon (Columba livia) : a study of the muscular system of the pigeon

Introduction

That the pigeon has a well-developed muscular system is shown by its rapid and sustained flight. These birds have been killed in New York whose crops contained undigested grains of rice that must have been swallowed in North Carolina or Georgia not long before. We are also familiar with their use as carriers of messages, in which their speed has been carefully and accurately timed and found to be truly remarkable. These and other instances of rapid flight and long endurance are accounted for when we come to inspect the muscles of flight and observe how well adapted they are by structure and development for that purpose. The pigeon, therefore, makes a very good subject for laboratory work when it is desired to dissect a representative of the order Avis.

In this sketch of the myology of the pigeon, the muscles are grouped in the following manner. Beginning with the muscles of the head, those which perform the movements of the mandible, ear and eye are described. In the next group the

4 INTRODUCTION.

muscles of the neck are dissected. In successive order the following groups are described. Those of the pectoral extremity, of the shoulder girdle and arm, of the hand, of the thorax and abdomen, of the trunk and thigh, of the front of the leg, of the back of the leg, and lastly the muscles of the tail.

Under the heading of each group a list of the muscles found in the group is given. It is hoped that this orderly discussion will assist the student not only in the work of dissection, but also in the more important end of acquiring a clear idea of the relative position of the several parts which go to make up the muscular system.

Before the student begins the study of the myology of the pigeon he should be thoroughly familiar with its osteology, an outline of which will be found in Dr. T. J. Parker 1 s Zootomy (vertebrata).

Myology of the Pigeon.

MUSCLES OF THE HEAD.

In this group will be found the muscles which have to do with the movement of the lower jaw, eye, ear, and tongue. In removing the skin of the head, the first muscle which makes its appearance is the Platisma Myoides, which closely adheres to the skin. After the removal of this, the muscles of the lower jaw are most prominent. These consist of the

Masseter.

Temporal.

Digastric.

En to-tympanic .

Pterygoides internus.

Pterygoides externus.

Platisma Myoides is a thin sheet of muscle found immediately beneath the skin. It covers the posterior and lateral portions of the head and has its origin in either side of the head, arising from that portion of the frontal bone which forms the posterior boundary of the orbital cavity, and also from the squamous portion of the temporal. From this origin, the fibres on either side pass backward and inward and meet at the point where the head joins the neck. The continuation of the muscle passes backward, covering the back and sides of the neck, and adhering closely to the skin into which it finally inserts. The fibres of the muscle, near its origin, are also attached to the skin of the external ear.

Masseter. — This is a small muscle' situated just in front of the orifice of the ear. It arises from the outer surface of the squamosal bone and passes obliquely downward and forward, and as it approaches the jugal bone it gives off a delicate tendon which passes over the outside of the jugal to insert into the articular portion of the mandible. The main portion of the muscle then passes on the internal side of the jugal to insert into the stipraangular portion of the mandible. The function of this muscle is to raise the lower jaw.

Temporal. This muscle is only exposed by carefully removing the entire eyeball. It arises by two sets of muscular fibres. The first portion arises from the base of the alisphenoid. The second portion arises from the upper surface of the paletine

MUSCLES OF THE HEAD. 7

and pterygoid bones. Both portions form a common insertion into the internal surface of the supraangular portion of the mandible. The function of this muscle is to close the lower jaw and to hold it firmly to its articulation.

Digastric. — This muscle has two distinct portions. The first portion arises from the exoccipital region of the skull, and passes obliquely downward and forward to insert into the posterior surface of the articular bone of the mandible. The second portion is entirely covered by the first portion, and arises from the tympanic portion of the squamosal ; from thence it passes directly to the articular bone of the mandible. It is the first portion of this muscle that is illustrated in Fig. 1.

EnTO-Tympanic is a small muscle situated at the base of the skull, the function of which is to raise the pterygoid region. It arises froirrthe rostrum and basi-sphenoid and passes backward to be inserted into the pterygoid and quadrate of the same side.

Pterygoides InTERNUS is a large muscle situated at the base of the cranium, arising from the palatine, sphenoidal rostrum, and pterygoid, and inserting into the inner surface of the ramus of the mandible as far back as the articular bone.

Pterygoides Externus. — This is smaller than, and concealed by, the preceding. It arises from the quadrate and pterygoid bones. It runs forward and outward to be inserted on the inner surface of the mandibular ramus.

MUSCLES OF THE TONGUE.

MUSCLES OF THE TONGUE.

These consist of certain muscles which are attached to the hyoid apparatus, and perform the different movements of the tongue. They consist of the

Mylo-hyoid,

Stylo-hyoid,

Genio hyoglossus,

Cerato-hyal,

Depressor-glossi.

Mylo-hyoid is a very delicate set of muscle fibres arising on either side from the anterior half of the lower margin of the jaw. The fibres from either side run transversely across to join in a median raphe. This muscle really forms the floor of the mouth, and supports the lingual and hyoid apparatus.

Stylo- hyoid. — This is a delicate slip of muscle which is seen lying on the outer side of the face. It arises from the external surface of the articular bone of the mandible, and passes to be inserted into the cerato-branchial of the thyro-hyal. When this muscle contracts it pulls the tongue to one side.

IO MYOLOGY OF THE PIGEON.

Genio-hyogix>ssus. — This is the largest of this group. It arises from the internal surface of the mandible at about the middle. The fibres form a flat band of muscle which passes obliquely downward and backward until it reaches the thyro-hyal, around which it courses and which it envelopes back to its posterior extremity. The function of this muscle is to thrust the tongue from the mouth.

Cerato-hyal is a slender muscle covering the thyro-hyal, along which it passes, following the course of the thyro-hyal and adhering to the hyoid until it reaches the uro-hyal, into which it is inserted. This muscle has also the function of moving the tongue to one side.

Depressor-glossi is an azigos or single muscle, and the smallest of the tongue muscles. It arises from the ventral surface of the basi-hyal and passes directly forward to the glosso-hyal. The function of this muscle is to depress the tip of the tongue and to elevate the base.

THE MUSCLES OF THE EYE. II

THE MUSCLES OF THE EYE.

It is advisable to leave the dissection of these muscles until after the dissection of the neck. For, in order to see them, a large portion of the skull must be cut away. The muscles of the eye in the pigeon consist of those muscles which perform the movements of the eyelids and ball. They are the

Orbicularis palpebrarum,

Pyramidalis nictitans,

Obliquus superior,

Obliquus inferior,

Rectus superior.

Rectus inferior,

Rectus externus,

Rectus intern us.

Orbicularis Palpebrarum. — This muscle consists of a few fibres which surround the external eyelids. In the upper eyelid the fibres are very indistinct, but on the lower they are distinct, because it is upon this lid that the action of the muscle is principally exerted. The eye is closed by the lower lid being drawn up.

Pyramidalis Nictitans. — In order to see this muscle it is necessary to take hold of the free edge of the nictitating membrane, or third eyelid, with the forceps and pull it backward over the eye. When the membrane is tense, it will be noticed that the free border is thicker than the rest of it. This thick part is really the tendon of the Pyramidalis nictitans. If this tendon is followed up, it will be found to spring from a little muscle which arises from the lower internal side of the eyeball. It soon gives off the tendon just spoken of, which passes through a pulley formed by another muscle, called the quadratus nictitans, whose function is to prevent the pyramidalis tendon from pressing on the optic nerve in its action. After the tendon passes through this muscular pulley, it passes downward to reach the lower extremity of the third eyelid, to which it is attached along its entire free margin. The action of this muscle is to pull the third eyelid over the eye.

Quadratus Nictitans is a small band of muscle fibres arising from the sclerotic of the upper side of the eye ball. Its fibres pass downward and inward to be inserted into the sheath of the optic nerve. The function of this muscle is to form a pulley for the Pyramidalis.

THE MUSCLES OF THE EYE. 1 3

Obliquus Superior. — The two oblique muscles arise close together, and will be easily recognized by their closely connected origins and their widely separated insertions. The obliquus superior arises from the antero-internal surface of the orbital plate of the frontal bone. Its fibres pass backward and upward to be inserted into the upper side of the eye ball.

Obliquus Inferior arises close to the preceding and forms a similarly shaped muscle. The fibres pass backward and downward to be inserted into the sclerotic of the inferior surface of the eyeball.

The Recti Muscles. — The four recti muscles will arise from that portion of the interorbital septum which forms the circumference of the optic foramen. The superior rectis arises from the superior border of this margin, the fibres pass forward, upward and outward to be inserted into the superior border of the sclerotic. The rectus inferior arises from the inferior portion of the foramen circumference. Its fibres pass forward, downward and outward to be inserted into the inferior surface of the sclerotic.

The rectus externus arises from the posterior ■nortion of the foramen circumference. Its fibres pass outward and backward to be inserted into the posterior surface of the sclerotic.

The rectus interims arises from the anterior surface of the foramen circumference, and its fibres pass outward and forward to be inserted into the anterior surface of the sclerotic of the eyeball.

PLATE I.

Fig. 4.

Fiq. 1.

THE MUSCLES OE THE EYE.

Indkx to Plate I., Fig. t. Index to Plate I., Fig. 4.

I. Platisma myoides

Flexor perforatus medius

Digastric.

secundus pedis.

Masseter.

Flexor perforatus indicis

Stylo-hyoides.

secundus pedis.

Genio-hyoid.

Flexor perforatus annulis

Cerato-hyal.

primus pedis.

Rectus capitis lateralis.

Flexor perforatus medius

Biventer cervicis.

primus pedis.

Complexus.

Flexor perforatus indicis

Ivongus colli posticus.

• primus pedis.

Obliquus colli.

Tendon of the Gastroch-

Inter transversales.

nemius.

Longus colli anticus.

Tendon of the Flexor longus hallucis.

Flexor profundus digitorum.

Soleus.

Plexor hallucis brevis.

Extensor hallucis brevis.

Biceps femoris.

External head of the Gastrocnemius thrown back.

Middle head of the Gastrochnemius thro w n back.

Internal head of the Gastrocnemius thro w 11 back.

Adductor longus.

Insertion of the Vastus extern us.

Femur.

THE MUSCLES OF THE NECK.

These consist of a superficial set of muscles which arise from the different cervical vertebrae and insert on the head, and of a deep set of muscles which connect the vertebrae with each other. They are the

Biventer cervicis.

Complexus.

Rectus capitis posticus.

Longus colli posticus.

Obliquus colli.

Rectus capitis lateralis.

Trachelo-mastoideus.

Rectus capitis anticus.

Longus colli anticus.

Inter spinales.

Inter transversales.

Biventer Cervicis arises partly from neighboring muscles and partly by a delicate tendon from the neural spine of the antepenultimate cervical vertebra. Its muscular origin is from the longus colli posticus. Its tendinous origin extends forward on the dorsal side of the neck in the

THE MUSCLES OF THE NECK. 1 7

median line, soon passing into a spindle-shaped belly about one and a half inches long, again becoming tendinous, succeeded by a second belly which inserts into the supra-occipital between the complexus and rectus capitis posticus.

Complexus arises from the transverse processes of the fourth, fifth and sixth cervical vertebrae. This extensive origin gives the muscle good breadth. It is inserted at the supra-occipital region, its insertion extending to the posterior median line where it blends with its fellow of the opposite side.

Rectus Capitis Posticus arises from the whole length of the spine of the axis, extends upward and is inserted below the supra-occipital margin. It is a thick, strong muscle found immediately below the complexus. Its function is to extend the head.

IvOngus Colli Posticus. — This is a long muscle extending the whole length of the back of the neck. Its origin is from the neural spine of the ante-penultimate dorsal vertebra, and by muscular slips from the lamina of the cervical vertebrae as far forward as the seventh. At its most posterior origin it blends with the fibres of the longissimus dorsi. It extends directly forward on the back of the neck to be inserted into the neural spine of the axis, blending somewhat at this place with the biventer cervicis.

Obliquus Colli consists of six muscular digitations. The first or posterior digitation arises from the transverse process of the eleventh cervical vertebra and inserts into the spine of the ninth cervical vertebra, and so each digitation arising from a transverse process inserts into the spine of the vertebra next but one in front of it ; the anterior four digitations unite with the three digitations of the longus colli posticus.

Rectus Capitis Lateralis is a triangular muscle situated at the front and side of the neck. It arises from the third, fourth and fifth cervical vertebrae, and passes obliquely upward to be inserted into the basi- and par-occipital regions. This muscle draws the head to the side and flexes it upon the neck.

Trachelo-Mastoideus. — This muscle is shaped somewhat like the preceding and arises in common with it, partly overlapping it in its course. It is inserted into the basi-temporal bone. Its action is similar to that of the rectus lateralis.

Rectus Capitis Anticus. — This is triangular and is situated in the front (ventral surface) of the

MUSCLES OF THE NECK. 19

neck. It arises from the ventral surface of the transverse processes and from the centrse of the second, third and fourth cervical vertebrae. It blends somewhat with the complexus and is inserted into the basi-temporal .

Longus Colli Anticus is a long muscle extending the whole length of the ventral side of the neck. It arises from the centrse and transverse processes of the posterior cervical vertebra, and inserts on the centrum of the atlas. The deep muscles of the neck are those which bind the different parts and processes of one vertebra to another. The most important of these are :

Inter-Spinales. — A series of muscles connecting the neural spines. They are best seen in those cervical vertebrae which have high spines.

Inter-transversales is a series somewhat similar to the preceding, but arranged in two sets. One set connects the transverse processes, the other connects the parapophyses. These muscles afford protection to the vertebral artery.

MUSCLES OF THE PECTORAL EXTREMITY.

In this group will be found certain cutaneous muscles lying in the alar membrane, the muscles forming the fleshy portion of the breast and the muscles of the arm. The group consists of the

Tensor Patagii lougus,

Tensor Patagii accessorius,

Tensor Patagii brevis,

Pectoralis major,

Pectoralis secundus,

Pectoralis tertius,

Pectoralis quartus,

Biceps,

Triceps,

Brachialis anticus.

In taking off the skin of the breast and arm, the student should be careful not to remove the patagii muscles situated in the wing or alar membrane.

Tensor Patagii Longus. — This is a subcutaneous muscle lying in the alar membrane. Its muscular fibres take their origin from the antero-external region of the pectoralis major muscle ; it

MUSCLES OF THE PECTORAL EXTREMITY. 21

receives fibres from a similar muscle, the tensor patagii brevis, and then gives off a long tendon which passes through the free border of the alar membrane to be inserted into the skin on the preaxial border of the manus.

Tendon Patagii Accessorius. — This is also a subcutaneous muscle, which lies in the posterior region of the alar membrane. It arises from the bicipital fascia, and also has fascial connection with the tendon of the tensor patagii longus. The belly of this muscle is quadrilateral, and gives off a long tendon which passes across the alar membrane till it reaches the free border of the membrane, where it passes parallel to the tensor patagii longus to be inserted with it into the skin of the preaxial border of the manus.

Tensor Patagii Brevis. — This muscle is situated on the dorsal aspect of the shoulder, consisting of a broad sheet of muscle fibres. It arises from the dorsal ends of the furcula and coracoid. It then passes backward, running alongside of, and partly covering, the triceps. It then has some connection with the tensor patagii longus, at which point it gives off a broad tendon, which is inserted into the fascia of the extensor carpi radialis longior at the elbow joint.

Pectoralis Major. — This is the muscle which forms the greater portion of the fleshy breast of the pigeon. It arises from the ventral part of the whole length of the keel of the sternum, from the body of the sternum and from the clavicle. It is closely connected with the pectoralis tertius, which it overlies. It is inserted by muscular fibres into the ventral aspect of the greater tuberosity of the humerus. The function of this muscle is to depress the wing.

Pectoralis Secundus (Sub-Clavius).— This is the bipinnate muscle, lying immediately beneath the muscle last described. Its fibres arise from the keel of the sternum and from the body of the sternum internal to the origin of the preceding muscle. Its fibres converge anteriorly, and form a round tendon which passes through the foramen triossium to be inserted on the outer side of the humerus, just below the insertion of the pectoralis major. The function of this muscle is to elevate the limb.

Pectoralis Tertius arises from the corpus sterni near the costal border, and forms a strong tendon which is inserted into the lesser tuberosity of the humerus. Its fibres are closely connected with those of the pectoralis major, except at its insertion.

MUSCLES OF THE PECTORAL EXTREMITY. 23

PECTOralis Quartus. — This muscle is the smallest of the pectorals, and is situated at the front of the breast. It arises by two heads, one from the dorsal extremity of the clavicle, the other from the dorsal surface of the manubrium of the sternum. The two heads unite to form a common insertion into the lesser tuberosity of the humerus, blending with the subscapularis at this point.

Biceps. — This is a long fusiform muscle occupying the antero-internal aspect of the brachium. It arises by two heads, one from the outer aspect of the head of the coracoid, just beyond the glenoid cavity. The other head arises from the ulnar tuberosity of the humerus. A common belly is formed whose tendon is inserted into the ulna, just in front and below the articular cavity. The function of this muscle is to flex the ante-brachium.

Triceps. — This muscle is a large one situated on the inner and hinder surfaces of the arm. It consists of two distinct bellies and three heads. The scapula or long head arises by a tendon from the rounded tubercle on the outer posterior margin of the glenoid cavity of the scapula. It forms a somewhat thick flat belly, which winds around the shoulder joint beneath the scapular portion of the deltoid, runs down the postero-lateral aspect of the humerus, having fascial connection with the external triceps. It then forms a flat tendon just above the elbow, where it is inserted into the radial side of the olecranon process of the ulna. The internal head arises on the inner margin of the pneumatic fossa, and unites below the fossa with the third or external head. This head of the muscle arises on the outer margin of the pneumatic fossa, forming a well-marked bifurcation to the common belly thus formed, the fibres of which make attachment to the posterior surface of the humerus, and from thence the muscle passes over the elbow joint to be inserted into the olecranon process of the ulna. The function of this muscle is to extend the ante-brachium. Brachialis AnTICUS is a small muscle arising from the anterior and inner side of the distal extremity of the humerus and inserting on the proximal end of the ulna immediately below the greater sigmoid cavity. It has the function of flexing the ante-brachium.

MUSCLKS OF THK TRUNK AND PECTORAL LIMB. 25

MUSCLES OF THE TRUNK AND PECTORAL LIMB.

The muscles of this group consist mainly of the muscles which bind the scapula to the body. They are, the

Latissimus Dorsi.

Trapezius.

Rhomboideus.

Levator Scapulae.

Serratus magnus.

Thoracico Scapularis.

Latissimus Dorsi is the most superficial of the muscles of the back in the scapular region. It arises from the spines of the last cervical and the first dorsal vertebrae, and extends as a thin band of muscle superficially over all the muscles of this region. Then it passes between the scapular and humeral parts of the biceps to be inserted into the hinder surface of the shaft of the humerus at about its middle.

Trapezius. — This muscle is found immediately beneath the preceding. It stretches across from the back to the scapula and helps to bind that bone firmly to the body. It arises from the neural spines of the last cervical and first four dorsal vertebrae, and inserts along the whole length of the vertebral margin of the scapula.

Rhomboideus is situated immediately beneath the preceding and has nearly the same origin and insertion. It arises from the neural spines of the first four dorsal vertebrae. Its fibres pass obliquely backward to insert along the posterior two-thirds of the vertebral margin of the scapula and also on the internal surface of that bone.

Levator Scapula is found immediately beneath the rhomboideus. It arises by muscular fibres from the transverse processes of the first two cervical vertebrae and inserts into the middle of the internal surface of the scapula.

Serratus Magnus arises by three fleshy digitations from the second, third and fourth dorsal ribs. These digitations unite to form a common band of muscle which inserts on the lower margin of the distal end of the scapula.

Thoracico Scapularis. — This is a muscle seen on the chest wall, anterior to the muscle just de-

MUSCLES OE THE TRUNK AND PECTORAL LIMB. 27

scribed. It arises by two fleshy digitations from the last free rib and the first dorsal rib. The two digitations unite to form a common belly which penetrates the subscapularis muscle to be inserted into the inner surface of the scapularis about its proximal fourth.

MUSCLES OF THE SHOULDER-GIRDLE AND ARM.

The shoulder-girdle of the pigeon consists or L ae scapula, clavicle and coracoid. So that under this head we will consider the muscles that arise from these three bones and insert into the humerus. They are the

Teres major.

Subscapularis.

Teres minor.

Coraco-brachialis.

Deltoid.

In order to see the muscles reaching from the shoulder girdle to the arm, it is necessary to take the entire shoulder-girdle and arm from the body. To do this one must cut the muscles binding the scapula to the body. Then disarticulate the coracoid from its sternal articulation and cut the clavicle near its sternal articulation with a pair of scissors. To expose the articulations of these bones the large pectoral muscle of the breast must be cut away from the sternum. These bones having been freed from the sternum, the shoulder-girdle and arm will come away from the body.

MUSCLES OF THE SHOULDER-GIRDLE AND ARM. 29

Teres Major. — This is the largest muscle attached to the shoulder-blade, or scapula. It arises entirely from the scapula, taking its origin from both the external and internal surfaces of the posterior two-thirds of its length. It is fusiform in shape and at first sight seems to cover the entire outer surface of the scapula. Its fibres are collected into a short, strong tendon, which passes to be inserted into the lesser tuberosity of the humerus and also into the margin of the pneumatic fossa.

Subscapulars. — Still examining the external surface of the scapula and using the teres major as a landmark, the muscle which is seen immediately in front of it is the subscapularis. This muscle arises from both the inner and outer surfaces oi the proximal half of the scapula, being partly covered over by the teres major. The fibres wind around beneath the inferior border of the scapula to the internal surface, where the fibres from the internal and external surfaces meet and form a short tendon, which passes to be inserted into the lesser tuberosity of the humerus in common with the teres minor and pectoralis quartus. The belly of the subscapularis is more or less divided by the insertion of the thoracico-scapularis.

Teres Minor. — Turning the scapula so that the internal surface may be viewed, and using the subscapularis as a guide, the muscle just in front of it is the teres minor. This muscle arises from the irternal surface of the anterior tip of the scapula, but mainly from the upper extremity of the clavicle, where it joins the scapula. Its fibres converge to form a very short tendon which is inserted, with the tendons of the subscapularis and pectoralis quartus, into the lesser tuberosity of the humerus.

Coraco-Brachiaus. — This muscle is quite a large one in comparison with the muscles just examined. It will be seen on the antero-internal surface of the coracoid bone. It arises from nearly the whole length of the bone and passes directly upward until it meets the tendons of the subscapularis and teres minor, where it gives off a small tendon to be inserted into the lesser tuberosity of the humerus, between the insertions of the teres major and subscapularis.

Deltoid. Turn the scapula over so as to view the external surface. A long muscle will be seen arising from the anterior end of the scapula and passing obliquely downward to the lower end of the humerus. This is one portion of the deltoid muscle, of which there are two parts. This part

MUSCLES OF THE SHOULDER-GIRDEE AND ARM. 3 1

arises from the external surface of the anterior end of the scapula and passes down the arm to be inserted into the external surface of the middle third of the humerus. The other portion of the deltoid muscle arises just in front of the preceding, but not from the same bone. It arises from the upper extremity of the coracoid bone, passes over the shoulder joint to be inserted into the greater tuberosity of the humerus.

32 MYOLOGY OF THF, PIGEON.

Index to Plate II , Fig. 2

1. Head of the triceps (humeral).

2. Extensor proprius pollicis.

3. Extensor indieis brevis.

4. Pectoralis major.

5. Tensor patagii longus.

6. Tensor patagii brevis.

7. Biceps.

8. Tensor patagii accessor! us.

9. Extensor metacarpi radialis longior.

10. Pronator brevis.

11. Pronator longus.

12. Flexor digitorum profundus.

13. F'lexor carpi ulnaris brevior.

14. Flexor digitorum sublimus.

15. Flexor carpi ulnaris longior.

16. Interossei.

17. Flexor brevis pollicis.

18. Flexor metacarpi brevis.

MUSCLES OF THE ANTE-BRACHIUM. 33

MUSCLES OF THE ANTE-BRACHIUM OR FOREARM.

The muscles of the forearm of the pigeon consist of flexors, pronators, extensors, and supinators. The flexors and pronators are situated on the inside of the forearm, while the extensors and supinators are on the outside of the limb. We will first consider the muscles on the inside of the forearm.

In taking off the skin of the inside of the forearm, the dissector will meet with a tendinous band on the ulnar side extending from the internal condyle to the wrist. This is a part of the flexor sublimus muscle, and must not be removed. The muscles, having been separated, will be found to occupy the following positions from above downward : The uppermost muscle is the extensor metacarpi radialis longior, with its two heads. As it is an extensor muscle, we will consider it when dissecting the outside of the forearm.

The muscle next below this is the pronator brevis, and immediately below this is the pronator longus. Below this and partly covered by it will be found the flexor digitorum profundus. Beneath and between the last two muscles mentioned, the flexor carpi ulnaris brevior is situated. Below the flexor digitorum profundus and partly covering it is seen the tendinous band spoken of above ; this is the flexor sublimus digitorum,and immediately beneath it will be found the flexor carpi ulnaris longior (Fig. 2.) The muscles then to be studied on the flexor side of the forearm, are the

Extensor metacarpi radialis longior.

Pronator brevis.

Pronator longus.

Flexor digitorum profundus.

Flevor carpi ulnaris brevior.

Flexor digitorum sublimus.

Flexor carpi ulnaris longior.

Pronator Brevis is the uppermost muscle on the flexor side of the forearm. It arises from a small tubercle above the external condyle of the humerus, crosses the forearm and inserts into the preaxial side of the shaft of the radius a short distance above its distal extremity.