This is a round cord-like muscle in which tendinous tissue predominates. It is placed in front of the gastrocnemius, which completely covers it.

Origin. - From a deep depression (supracondyloid fossa) at the inferior and posterior part of the femur. In passing down the leg the tendon of this muscle gets behind the gastrocnemius tendon by winding round its inner side. It then spreads out and becomes attached by means of short tendinous slips to either side of the point of the hock to which it now forms a cap. A small synovial bursa is interposed between the two parts to facilitate the movement of one upon the other.

Insertion. - Continuing its course down the back of the canon it ultimately divides into two branches and becomes inserted into the upper and posterior part of the second phalanx or small pastern-bone. The perforans tendon passes between these two branches on its way to the foot.

Action. - To flex the pastern on the fetlock-joint, and extend the hock on the tibia.