A. Extensor Division

IV. Muscles of the Forearm

The extensor carpi radialis is like that of the horse. There is sometimes a small muscle lying along its inner border, which may represent the extensores pollicis.

There are three digital extensors: 1. The common or anterior digital extensor (M. extensor digitalis communis) arises by two heads from the extensor epicondyle and the ulna. The heads fuse about the middle of the forearm, and terminate soon on a tendon which passes over the carpus and metacarpus, gradually inclining forward. At the fetlock joint it divides into two branches, which are inserted into the third phalanges. 2. The internal digital extensor (M. extensor digiti tertii proprius) arises on the extensor epicondyle, and is inserted by two branches into the second and third phalanges of the inner digit. The tendon receives two reinforcing slips from the suspensory ligament. 3. The lateral digital extensor (M. extensor digitalis lateralis s. digiti quarti proprius) arises from the external lateral ligament of the elbow joint, the external tuberosity of the radius, and the ulna. The tendon terminates like that of the preceding muscle.

The extensor carpi obliquus resembles that of the horse.

The extensor tendons are bound down at the carpus by an annular ligament, and are furnished with synovial sheaths (Figs. , ).