The surgical anatomy of the horse

PART II.-FORE LIMB New York

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Preface To Part II

Owing to the greater surgical importance of the limbs in veterinary practice, consecutive treatment has been dealt with a little more fully in this volume than in Part I., otherwise precisely similar lines have been followed.

To the Vice-Chancellor of the University of Liverpool the author desires again to express his gratitude for the ever-ready advice and kindly help, of which it has been the author's good fortune to avail himself.

The onerous task of revising and correcting the proofs has been kindly undertaken by the author's friend and former colleague. Professor Macqueen, many of whose views upon matters appertaining to the purely surgical part of the work have been adopted. Although these have been frequently acknowledged throughout this volume and were referred to in the General Preface to Part I., the author feels it his duty to make reference to them here, for to have had the collaboration of one with the ripe experience of Professor Macqueen cannot fail to add materially to the practical value of the work.

The kind reception accorded the first volume by the majority of the critics and by practitioners generally in this country, and especially by his fellow veterinarians in France and America has been most gratifying to the author, and has convinced him that his opinion of the necessity which existed for a work of the kind, as expressed in the Pretace to Part I., was well founded.

It was pointedly remarked bv one esteemed reviewer, presumably a member of our sister profession, that "since 1832. when William vi PREFACE

Percival produced the first work exclusively devoted to the anatomy of the horse, considerable advances have been made in the methods of teaching veterinary anatomy ; but it cannot be said that the production of anatomical literature has been correspondingly abundant in this country. The veterinarian has not had his time too heavily taxed by the examination of frequent new publications." The justice of this soft impeachment is best known to the members of the veterinary profession, and the intended mission of the writer will therefore be amply fulfilled if the effort be considered by his fellow workers to be a useful contribution to this unfortunately too inadequate supply of veterinary literature.

To the judgment of practitioners, who are best qualified to know their own wants, and at whose hands the first part of this work was so charitably received, without further remark this volume is now committed.

Department of Veterinary Anatomy,

Contents

PART II— THE FORE LIMB

CHAl'. l.^OE

I. SUPERFICIAL EXAMINATION i

Chapter I Superficial Examination

The student should first examine the outer aspect of the region of the shoulder, and endeavour as near as possible to locate the outhne of the scapula. Having done this, it vv^ill be observed that running obliouely downwards and forwards over the area enclosed by the imaginary outline drawn, there*are four elevations, which are formed by the following muscles :

The most superior or anterior elevation indicates the position of the supraspinatus muscle, which lies in the supraspinous fossa and is attached inferiorly to the anterior divisions of both tuberosities at the proximal end of the humerus. Between the two tendons of insertion of this muscle the tendon of origin of the biceps emerges. The second elevation is formed by the infraspinatus muscle. This muscle has two tendons of insertion also, one of which is attached to the inner side of the convexity {i.e., the more posterior of the two divisions of the external tuberosity), whilst the other tendon plays over the outer aspect of the convexity and is inserted into the upper extremity of the deltoid ridge. A small synovial bursa is placed between this tendon and the outer surface of the convexity. Between the two muscles named, the tubercle of the spine of the scapula may be easily located. It is important to note that the tendons of the supraspinatus and infraspinatus muscles by their disposition materially assist in keeping the head of the humerus in the glenoid cavity of the scapula. These muscles are affected in suprascapular paralysis, and it will be seen that when this affection has advanced to such a degree that the muscles become atrophied, the long axes of the muscles and their tendons become considerably increased in length on account of the diminution in width of the bellies. This increased length causes a relaxation of the parts, with the result that we have one of the diagnostic symptoms of suprascapular paralysis, viz., free external rotation of the head ot the humerus. Internal rotation is prevented by the tendon of the subscapularis muscle, which is not affected in this paralysis. The two posterior elevations are formed by the underlying deltoid muscle, which arises from the posterior border of the scapula and is inserted into the deltoid tubercle of the humerus. The appearance of two elevations is due to a false septum in the muscle caused by a dipping inwards of the scapular fascia which binds this muscle to the preceding one and to the underlying bone.

The point of the shoulder is formed by the coracoid process of the scapula. This should be carefully palpated, since it is a common seat of fracture, particularly in young animals, the fracture being usually due to the shoulder being caught in a doorway or narrow gateway. Running over the shoulder joint and spreading out as it descends is the mastoido-humeralis muscle. Inferiorly to the shoulder this muscle again becomes narrower, and runs to its insertion into the outer lip of the musculo-spiral groove. Near the upper border of the mastoido-humeralis and just in front of the point of the shoulder is the common seat of " shoulder tumour " or " abscess."

The long axis of the scapula runs downwards and forwards, and meets the long axis of the humerus, which runs downwards and backwards forming an acute angle at the shoulder joint. The triangle, of which these two bones form the antero-superior and antero-interior sides, is filled by a large muscular mass which is indicated on the exterior by a well-marked convex bulging of distinct outline. This mass is formed by the triceps extensor cubiti or caput muscles, which are inserted into

^ 7

Plate I. — Outer Aspect of Shoulder and Arm

I. Elcvaiion formed by caput muscles. 2. Point of elbow (summit of olecranon process ot ulna). 3. Position! of elbow articulation. 4. Elevation formed by flexor metacarpi externus muscle. 5. Elevation formed by extensor pedis. 6. Elevation formed by extensor metacarpi magnus. 7. Groove between brachialis anticus and mastoido-humeralis. S. Point of shoulder, g. Groove in front of or above supraspinatus muscle.

SUPERFICIAL EXAMINATION the summit of the olecranon process, and are the great extensors of the elbow. The marked convexity of these muscles should be observed, since in advanced cases of radial paralysis or " dropped elbow," in place of the convexity we have a marked depression, due to the fact that these muscles have become atrophied.

What is commonly known as the " point " of the elbow corresponds to the position of the summit of the olecranon process of the ulna. The elbow joint is placed from three to four inches downwards and forwards from this point, varying, of course, according to the size of the animal, and is indicated externally by a slight depression. It will be observed that there is an almost entire absence of muscular tissue on the outer aspect of the joint, which is here therefore very badly protected, a fact which renders it necessary to treat wounds in the neighbourhood of the joint with great care ; otherwise an open arthritis of the joint is a very liable complication.

Passing the hand down the front of the forearm, a very prominent and well-defined elevation is felt. This raised surface corresponds to the bellies of two muscles, the more anterior of which is the extensor metacarpi magnus, whilst the other is the extensor pedis. Behind the extensor pedis is placed the flexor metacarpi externus muscle, which is indicated externally by a slight and elongated elevation. Between these two muscles is situate the extensor suffraginis muscle, which does not provide any superficial marking, since it is wedged in somewhat tightly between the two muscles named. The tendons of the extensor pedis and extensor metacarpi magnus run over the front of the knee after having passed through the two vertical grooves on the anterior aspect of the inferior extremity of the radius, whilst that of the extensor suffraginis passes through a groove on the outer side of the inferior extremity of this bone. The tendon of the flexor metacarpi externus will be found to terminate just above the knee and on its postero-external aspect, where we feel a well-marked, hard ridge. This ridge corresponds to the upper border of the pisiform bone, and it should be remarked that this edge of the pisiform is almost immediately subcutaneous — a point which is of considerable surgical importance in dealing with affections of the knee which require tight bandaging for any considerable length of time. In such cases the pressure of the bandage should be taken off the edge of the pisiform bone by applying a roll of cotton wool or tow on either side ; otherwise the continuous pressure on the skin over the sharp edge of the bone will lead to a serious complication in the form of the bone making its appearance through the skin.

The outermost bones of the two rows of the carpus, namely the cuneiform and the unciform, should next be felt, and below the unciform the head of the outer small metacarpal or " splint " bone will be detected, from which without any difficulty the finger may be passed along the groove which corresponds to the line of apposition of the large and outer small metacarpal bones. This groove indicates the most common situation of splints, and particular familiarity should be made with it immediately below the knee, for here we find what are known as " knee splints," which are the most troublesome form of this affection.

Between the knee and the fetlock it will be found that the anterior aspect of the large metacarpal bone is immediately subcutaneous, but towards the outer side of this aspect the tendon of the extensor pedis muscle may be easily felt, and externally to that again the tendon of the extensor suffraginis muscle. At a point which is distant from two and a half to three and a half inches below the knee and immediately behind the small metacarpal bone there will be felt a slight thickening, which indicates the position where the subcarpal or check ligament unites with the tendon of the deep flexor of the digit, and which thickening must not be mistaken for fibrous enlargement due to a chronic sprain of the tendon. By taking up the foot and flexing the knee, the edge oi the ligament becomes much more evident to the touch.

The next step is carefully to manipulate the skin over the back tendons, namely, those of the flexor perforatus and flexor perforans

Plate II. — Right Foke Limb. Outer Aspect I. Position of elbow articulation. 2. Fle.xor inetacarpi e.xternus. 3. Elevation caused by pisiform bone. 4. E.xternal small metacarpal bone. 5. Edge of tendon of flexor perforans. 6. Level ot bases of sesamoid bones. 7. Situation of pastern joint. 8. Os suffraginis. 9. Position of fetlock articulation 10. Large metacarpal bone. 11. Edge of radius. 12. Elevation formed by belly of e.xtensor pedis, ij. Elevation formed by belly of extensor metacarpi magnus.

SUPERFICIAL EXAMINATION 5

muscles. These tendons should be felt as far as possible throughout their length, beginning at the knee, immediately below which they will be found at the spot where they leave the carpal arch. Just above the fetlock the tendon of the deep flexor will be found to disappear, for it here enters the fibrous ring formed for its passage by the perforatus tendon. The perforans, however, will be felt to make its reappearance just below the joint, where it emerges from the fibrous tube mentioned.

Careful manipulation of the outer side or the fetlock will reveal the presence of a hard, flat band which runs downwards and forwards to the anterior aspect of the limb, where it joins the tendon of the extensor pedis muscle. This band is the external division of the suspensory ligament, which has divided just above the fetlock after traversing the channel formed by the large and two small metacarpal bones. This slip of the suspensory ligament will be found to broaden out and to become much less apparent to the touch as we descend to its insertion. It is sometimes ruptured, particularly in young animals. Near where the suspensory ligament divides the small metacarpal bone will be found to terminate in a small rounded nodule. This is known as the " button " or the splint bone, and must not be mistaken for a splint.

The upper part of the inner aspect of the limb is best examined on a dead specimen. The limb should be disarticulated at the shoulder joint, and the inner cutaneous incision should be made as high up as possible in the armpit. The first point we notice is the curve indicating the inferior border of the posterior superficial pectoral muscle. This in most animals may be distinctly seen, but in all it may be easily felt. Extending vertically, and almost in the middle line of this aspect, will be felt an osseous ridge. This is the inner edge of the radius. Behind this ridge is a vertical groove, and posterior to the groove again we have a vertically elongated elevation which corresponds to the position of the belly of the flexor metacarpi internus muscle.

Just above the lower edge of the posterior superficial pectoral muscle and in a line with the ridge of the radius, if a little pressure be applied, the posterior radial artery may be located in the living subject by its pulsation, which may be more easily felt if the limb be drawn a little forward. This is a very popular seat for the taking of the pulse. It is also the seat of neurectomy of the median nerve, which will be referred to later.

Anterior to the ridge of the radius we see the inner aspect of the elevation formed by the extensor metacarpi magnus, to which reference has already been made. In the inferior third of the forearm we have the " chesnut,' a horny excrescence which upon manipulation will be found to be confined to the skin. The inner surface of the scaphoid and trapezoid, the innermost bones of the two rows of the carpus, should now be felt, and the faint depression between them noted.

Below the knee the tendons of the perforatus and perforans make their appearance, and may be felt as they are leaving the carpal arch. It is scarcely necessary here to impress the student with the importance of making himself quite familiar with these tendons, particularly where the check ligament joins the perforans, again immediately above the fetlock, and lastly just below this joint, wTiere the perforans is leaving the ring formed by the perforatus, since at these situations the tendons are most commonly sprained. If the knee be flexed and the flexor tendons pushed aside, the suspensory ligament may be felt in the channel formed by the large and small metacarpal bones.

By the application of pressure with the palmar aspect of the medius finger to the outer or inner side of the most prominent part of the fetlock, the plantar nerve may be rolled beneath the finger about half an inch posteriorly to the middle line. This should be practised, since it is of utility in deciding the seat of plantar neurectomy. The most prominent point at the back of the fetlock presents another horny

Plate III.— Inner Aspect of "Off" Fore Limb I. Edge of posterior superficial pectoral muscle. 2. Median nerve exposed. 3. Elevation formed by flexor metacarpi internus. 4. Elevation formed by extensor metacarpi magnus. 5. Chestnut. 6. Ridge of the Radius. 7. Position of ridge of pisiform bone. S. Internal plantar nerve exposed. 9. Digital nerve exposed.

SUPERFICIAL EXAMINATION 7

excrescence called the " ergot," surrounded by a tuft of long hairs. Subjacent to the skin and tendons in this position are the two sesamoid bones, the location of which may be decided by the fact that they move slightly towards the middle line upon the application of pressure to the outer surface of each with the thumb and finger.

Immediately below the sesamoid bone on either side of the limb is a depression in which the edge of the perforans tendon may be felt, and which is the seat of inferior plantar, or more correctly digital, neurectomy.

The region of the pastern should next be grasped with the hand, in order that the observer may familiarise himself with the conformation of the long pastern bone or os suffraginis.

It will be found helpful if, whilst making this examination, the student has a dried bone near, in order that he may compare the buttress-like processes at the upper extremity of the bone with the elevations formed by them in the limb. The palmar aspect of the hand should be passed over this region several times, until the student has quite satisfied himself by comparison with the dried bone that these elevations are normal. The next point of importance is the position of the pastern joint, which will be found about an inch to an inch and a half above the line of junction of the skin and hoof This joint is covered anteriorly by the flattened-out tendon of the extensor pedis. There is no anterior common ligament, so that the tendon is next the joint and gives support to the synovial membrane. Posteriorly the joint is well protected by the fibro-cartilaginous pad which projects upwards from the superior extremity of the back of the os coronae. According to Hunting's classification of ringbones, this joint is the seat of the class designated by the term " high," the " low ringbones " being those which affect the corono-pedal joint. The so-called false ringbones are placed on the suffraginis or corona", but do not affect the joints. By carefully manipulating the top of the hoof, the upper borders of the lateral cartilages will be felt. These cartilages, so far as they project above the hoof, should be traced out, and it should be noted that the greater part of the cartilage is placed within the hoof. If the foot be taken up in the living animal and the cartilages placed between the thumbs, the palmar aspect of the hands being applied to the wall of the hoof, a little pressure will distinctly reveal their elasticity.

Chapter II Superficial Dissections Outer Aspect Of Limb

Such a dissection is represented in Plates IV. and V., and the structures exposed are as follows :

The Bones

Near the upper end of the limb, the spine of the scapula (2) is seen running obliquely downwards and forwards. Towards its middle it shows the prominence called the tubercle of the spine (4), which gives attachment to the trapezius muscle. This muscle has been dissected away to expose the muscles lying beneath it. The summit or anterior portion of the outer tuberosity of the humerus (12) is visible, and to it the outer tendon of the supraspinatus muscle (6) is attached. Extending downwards and backwards from the summit is the deltoid ridge (13), which terminates inferiorly in the well-marked deltoid tubercle. The ridge is partially concealed by the insertion of the infraspinatus muscle (5).

Taking an oblique course downwards and backwards along the line of direction of the deltoid ridge, we arrive at the summit of the olecranon process of the ulna, which forms a marked and well-defined prominence (19).

The bones of the forearm are almost completely clothed by the extensor and flexor muscles of the metacarpus and digit. The lo THE SURGICAL ANATOMY OF THE HORSE

inferior extremity of the radius will, however, be found to be immediately subcutaneous between the tendon of the extensor pedis (22) and that of the extensor suffraginis (25).

Between the knee and fetlock almost the whole of the outer surface of the external small metacarpal bone (32) is represented, as is also the shaft of the large metacarpal, excepting that portion which is concealed by the tendons of the extensor pedis and extensor suffraginis muscles.

Below the fetlock we see the os suffraginis (46), the greater part of the front and lateral aspect of this bone being visible, together with the external prominence at its lower extremity.

The Ligaments

Only two ligaments are shown in the plates representing this aspect of the limb.

The Superior Sesamoulean or Great Suspensory Ligament (44). — This first makes its appearance about four inches below the knee. It is visible owing to the body of the outer splint bone having become so much thinner than it is above this point.

The ligament runs down the limb in the channel formed by the large and two small metacarpal bones. Just above the fetlock it splits into two parts. The outer division is plainly represented (44). It runs round the outer lateral aspect of the fetlock, and gives off a slip of insertion to the sesamoid bone of its side. It then runs obliquely downwards and forwards across the shaft of the first phalanx to the front of the limb, where it terminates by uniting with the tendon of the extensor pedis.

The Suhcarpal or Check Ligament. — This is placed behind the suspensory ligament just below the knee. Like the former ligament, its upper portion is concealed by the greater thickness of the upper extremity of the small metacarpal bone. It is the downward con-

SUPERFICIAL DISSECTIONS ii

tinuation of the posterior common ligament of the knee, and becomes united to the tendon of the flexor perforans about three and a half inches below the carpus. Along its outer edge is seen to run the external metacarpal vein (32).

The Muscles and Tendons

The Supraspinatus Muscle (6). — This occupies the whole of the fossa in front of, or above the spine of the scapula, which bears the same name. Its outer tendon of insertion, which is attached to the summit of the external tuberosity of the humerus, is represented in the plate (12). The muscle is a powerful extensor of the shoulder joint, and is supplied by the suprascapular nerve.

The Infraspinatus Muscle (5). — Occupies almost the whole of the infraspinous fossa. The outer surface of the muscle presents a depression which runs obliquely downwards and forwards, and which is somewhat deceptive in suggesting the possession of two bellies.

It is inserted by an inner tendon into the convexity of the external tuberosity of the humerus and by an outer broad tendon (8), which is represented in the plate, into the upper portion of the deltoid ridge. This muscle is an abductor and outward rotator of the humerus, and is supplied by the suprascapular nerve.

The Deltoid Muscle (9). — This muscle is also traversed obliquely downwards and forwards by a depression in which the scapular fascia dips. It arises from the dorsal angle and part of the posterior border of the scapula, and also from the scapular fascia. It is inserted into the deltoid tubercle. Its action is similar to that of the infraspinatus, and it is supplied by the circumflex nerve.

The Biceps (16). — In front of the upper half of the humerus we find the biceps muscle, which is seen to arise from the coracoid process. Its tendon passes through the bicipital groove between the tendons of insertion of the supraspinatus muscle. The biceps is inserted into the bicipital tuberosity of the radius.

The upper part of the biceps is visible owing to the fact that the mastoido-humeralis has been almost completely removed. Two or three inches of the last-named muscle are, however, represented near its insertion into the external lip of the musculo-spiral groove (i8).

Behind this piece of the mastoido-humeralis is noticed part of the Brachialis Anticus Muscle (17), which arises at the back of the upper extremity of the humerus. It then winds round the outer side of the bone in the musculo-spiral groove, where it is represented in the plate (17). Its tendon of insertion, which is not visible, passes inwards beneath the internal lateral ligament of the elbow to be inserted into the radius and ulna.

The Triceps Extensor Cubki. — Two divisions of this muscle are represented here, namely, the large and middle heads (7 and 1 5).

The Caput Magnum (7) arises from the dorsal angle and glenoid edge of the scapula, and is inserted into the summit of the olecranon process of the ulna. This muscle fills up the greater part of the triangle of which the scapula (inferior border) and humerus form two of the sides. It is a powerful extensor of the elbow and a flexor of the shoulder.

The Caput Medium (15). — This division arises from the curved roughened line which runs upwards on the back of the humerus from the deltoid tubercle to the articular head. The upper part of the origin of the muscle is concealed by the deltoid. It is inserted with the large head, and is an extensor of the elbow.

Both these divisions of the triceps extensor cubiti are supplied by the musculo-spiral nerve.

In the region of the forearm quite a number of muscles are represented.

The Extensor Metacarpi Magnus (20). — This is the most anterior of the muscles here shown. Its belly, together with that of the extensor

Plate IV.— SUPERFICIAL DISSECTION.

Fore Limb (right), Outer aspect. — i. Cartilage of prolongation. 2. Spine of scapula. 3. Dorsal angle of scapula. 4. Tubercle of spine. 5. Infraspinatus muscle. 6. Supraspinatus. 7. Caput magnum. S. Tendon of infraspinatus. 9. Deltoid muscle. 10. Outer tendon of supraspinatus. 11. Insertion of deltoid. 12. Anterior division of external tuberosity of humerus (i.e., the summit). 13. Upper portion of deltoid ridge. 14. Tendon of origin of biceps. 15. Caput medium. 16. Biceps muscle. 17. Brachialis anticus. 18. Insertion of mastoido-humeralis. 19. Insertion of caput muscles into summit of olecranon process of ulna. 20. Extensor metacarpi magnus. 21. Flexor metacarpi externus. 22. Extensor pedis. 23. Ulnar accessorius.

SUPERFICIAL DISSECTIONS 13

pedis, forms the bulging mass in front of the forearm, which is so distinctly visible in the living animal.

It arises from the roughened ridge above the external condyle of the humerus, and its muscular portion gradually tapers as we descend to within two or three inches of the knee, where it is succeeded by a tendon. The latter passes under the extensor metacarpi obliquus and through the middle groove on the front of the lower extremity of the radius. It next crosses the knee in a vertical direction, where it lies on the anterior common ligament, and runs to its insertion into a roughened area at the front of the upper extremity of the large metacarpal bone. This muscle is the principal extensor of the knee joint, and its nerve supply is derived from the musculo-spiral.

The Extensor Pedis (22). — This is placed behind the extensor metacarpi magnus. It arises trom the small depression which is placed to the b outer side of the coronoid fossa, from the external lateral ligament of the r^ elbow and from the upper portion of the outer aspect of the radius. ij

Its muscular portion tapers at both ends, and inferiorly it is succeeded ^■ by a tendon which plays over the broad origin of the extensor metacarpi ^ obliquus. It next passes through the outer of the two vertical grooves T on the front of the radius, and crosses the knee under the annular band -^ of fascia, being superficially placed to the anterior common ligament. r>

The tendon is divisible into two portions — the outer and smaller of which joins the tendon of the extensor suffraginis. The inner and larger tendon plays over the fetlock and pastern joints and takes the place of an anterior common ligament of the latter, the synovial membrane of the pastern joint being supported by the posterior face of the tendon. The tendon then receives the two divisions of the suspensory ligament, and becomes inserted into the pyramidal process of the pedal bone. This muscle extends the knee, fetlock, and inter-phalangeal joints, and is supplied by the musculo-spiral nerve.

The Extensor Sujfraginis (25). — This is a small muscle which is placed between the extensor pedis in front and the flexor metacarpi externus behind. It arises from the external lateral ligament of the elbow, from the outer side of the upper end and outer border of the radius, and from the line of junction of the radius and ulna.

Its thin muscular portion is followed by a tendon which plays through the vertical groove on the outer aspect of the inferior extremity of the radius. It then crosses the outer side of the knee, passing through a synovial sheath. From the fibrous arch of the knee it receives a reinforcing band, and is joined by the portion of the tendon of the extensor pedis already referred to. It runs down the limb parallel to the extensor pedis, and is inserted into the upper extremity of the anterior face of the os sufFraginis.

This muscle extends the knee and fetlock, and is also supplied by the musculo-spiral nerve.

The Extensor Metacarpi Obliquus (24). — This is a small muscle which arises from the inferior portion of the outer aspect of the radius. At its origin the muscle is broad and flat, and it is here crossed by the extensor pedis.

Its tendon plays over that of the extensor metacarpi magnus, passes through the oblique groove at the inferior extremity of the radius, and runs downwards and inwards to be inserted into the head of the inner small metacarpal bone.