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.

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.

The supinator has been found by Arloing and Lesbre, but is usually absent in the pig.

The pronator teres is a small muscle which lies on the internal lateral ligament of the elbow. It arises from the internal epicondyle of the humerus, and reaches about to the middle of the inner border of the radius.

The flexor carpi internus is well developed. It arises on the flexor epicondyle of the humerus, and is inserted into the third metacarpal bone.

The flexor carpi medius is narrow and has no ulnar head.

The flexor carpi externus (M. extensor carpi ulnaris) is covered by a thick, tendinous band, which extends from the extensor epicondyle to the accessory carpal bone and outer aspect of the carpus. The tendon of the muscle perforates this band in the distal part of the forearm and ends on the proximal end of the fifth metacarpal bone.

The superficial digital flexor has two bellies. The tendon of the superficial head passes down behind the posterior annular ligament of the carpus (bound down by a special annular ligament), forms a ring at the fetlock for a tendon of the deep flexor, and ends by two branches on the second phalanx of the fourth digit. The tendon of the deep head, after detaching a slip to the tendon of the deep flexor, passes down with the latter (for which it forms a ring), and ends on the third digit.

The deep digital flexor has three heads—humeral, ulnar, and radial. The common tendon divides into four branches, the larger central pair ending on the third phalanges of the principal digits, the smaller pair on the accessory digits. The latter are bound down by a peculiar spiral band. There is no check ligament.

The lumbricales are represented by bundles which extend from the deep flexor tendon to the tendon of the deep head of the superficial flexor.

The third and fourth interossei are present. Each sends two slips to the corresponding sesamoid bones and extensor tendon.

There are flexors, adductors, and abductors of the second and fifth digits.

Muscles of the Pelvic Limb