This muscle lies on the outer part of the fore-arm, inclining to the front and immediately behind the extensor metacarpi magnus. It consists of two unequal portions, each having a separate tendon.

Origin. - From the outer and lower part of the humerus, the lateral ligament of the elbow-joint, and the upper and outer part of the radius.

The two tendons of this muscle pass over a groove in front of the lower end of the fore-arm, then over the front of the knee-joint, where they are enclosed in a synovial sheath and bound down by the annular ligament of the knee. On reaching the canon, the outer tendon joins with that of the extensor suffraginis. The inner and main division proceeds downward over the front of the large metacarpal bone to the fetlock-joint, where it-plays over a small synovial bursa. Lower down it is closely attached to the os suffraginis, or large pastern-bone, in the middle of which two branches of the suspensory ligament-an inner and outer-join it. Thus reinforced, it passes over the small pastern and enters the hoof.

Insertion. - Into the pyramidal process of the os pedis, or foot-bone.

Action. - To extend the fetlock on the canon and the knee on the fore-arm.