Situated immediately behind the biceps. A long fleshy muscle arising by two heads, and extending from the summit of the haunch to the superior part of the tibia.

Origin. - By one head from the spines of the sacrum and the sacro-sciatic ligament, and by the other from the tuberosity of the ischium.

Insertion. - Into the crest of the tibia and the fascia of the leg.

Action. - To flex the stifle and rotate the leg inwards. It also assists in the act of rearing, and braces up the fascia of the leg in support of the muscles.