Part 107

The =latissimus dorsi= is attached to the four ribs preceding the last. It is inserted into the internal lip of the bicipital groove.

The =mastoido-humeralis= divides into two parts, the =cleido-mastoideus= and =cleido-occipitalis=, which arise on the mastoid process and occipital crest respectively, and unite at the fibrous vestige of the clavicle.

The =anterior superficial pectoral= is thin. The =posterior superficial pectoral= is divided into parts, one of which ends on the humerus, the other on the fascia of the forearm.

The =deep pectoral= is clearly divided into two parts. The =scapular portion= resembles that of the horse, but its origin does not extend behind the first two chondro-sternal joints. The =posterior deep pectoral= is very long.

The cervical portion of the =serratus magnus= is greatly developed, its origin extending from the wing of the atlas to the upper part of the fifth rib, and passing under the thoracic portion; the latter resembles that of the ox.

MUSCLES OF THE SHOULDER

The =deltoid= is undivided; it arises from the aponeurosis covering the infraspinatus, and it ends largely on the deltoid ridge, but partly on the fascia of the arm.

The =supraspinatus= is large; it ends chiefly on the external tuberosity of the humerus.

The =infraspinatus= is inserted into a depression below the posterior division of the external tuberosity.

The =teres minor= is well developed; it ends on a tubercle between the external and deltoid tuberosities of the humerus.

The =subscapularis= and =teres major= have no remarkable features.

The =coraco-brachialis= is short and undivided.

The =capsularis= is very small and frequently absent.

MUSCLES OF THE ARM

The =biceps brachii= is fusiform and not greatly developed. Its tendon of origin is rounded and passes through the capsule of the shoulder joint. The tendon of insertion is bifid, ending on the radius and ulna.

The =brachialis= is well developed, and also ends on the radius and ulna.

The =tensor fascias antibrachii= resembles that of the horse.

The =long head of the triceps= is divided into two parts, except at its distal end, under which there is a synovial bursa. The =external head= is inserted into a crest on the outer surface of the olecranon by a thin tendon, under which there is a bursa. The =internal head= arises near the head of the humerus, beneath the coraco-brachialis.

There are two =anconei=.

MUSCLES OF THE FOREARM AND DIGITS

The =extensor carpi radialis= is a strong, fleshy muscle, the tendon of which is inserted into the proximal end of the third metacarpal bone. It may be divided into two parts (M. extensor carpi radialis longus, brevis).

The =extensor carpi obliquus= is well developed; it ends on the second metacarpal bone.

There are three (or four) =digital extensors=.

1. The =common= or =anterior digital extensor= (M. extensor digitalis communis) arises on the extensor epicondyle of the humerus and the lateral ligament of the elbow, and divides into three parts. The tendon of the =inner part= divides into two branches which end on the =second= and =third digits=; the tendon to the second digit is small and often absent. The tendon of the =middle part= divides lower down into two branches for the =third= and =fourth= (chief) =digits=; above this bifurcation it detaches a small branch to the =second digit=, which usually unites with the tendon of the extensor indicis. The tendon of the =deep head= divides into two branches, the inner one joining the tendon of the middle head, while the outer one ends on the =fifth digit=.

FIG. 227.—MUSCLES OF ANTIBRACHIUM AND MANUS OF PIG, ANTERO-EXTERNAL VIEW.

a, a′, Extensor carpi radialis; b, extensor carpi obliquus (s. abductor pollicis longus); c, d, e, common or anterior digital extensor; c′, c″, tendons of insertion of c; d′, d″, tendons of d; e′, e″, tendons of e; f, tendon of extensor indicis; g, extensor digiti quarti; h, extensor digiti quinti; h′, tendon of h; i, tendinous, and k, fleshy part of flexor carpi externus; k′, tendon of k; l, ulnar head of deep digital flexor; m, superficial digital flexor; n, brachialis. (After Ellenberger, in Leisering’s Atlas.) ]

2. The =extensor of the second digit= (M. extensor indicis proprius) is covered by the preceding muscle, with which it is partially fused. It arises on the ulna. Its delicate tendon usually unites with the tendon of the middle head of the common extensor which goes to the =second digit=.

3. The =lateral digital extensor= (M. extensor digitalis lateralis) consists of two distinct parts: (1) The large =dorsal= (anterior) =muscle= (M. extensor digiti quarti proprius) has a long tendon which ends on the =fourth digit=, and often sends a slip to the fifth digit. (2) The small =volar= (posterior) =muscle= (M. extensor digiti quinti proprius) ends by a long tendon on the lateral aspect of the =fifth digit=.