Overview
In the horse it has two heads: a vertebral head from the first caudal vertebrae and the broad sacrotuberous ligament, and a pelvic head from the ischial tuberosity. It runs down the caudal border of the thigh, between the biceps femoris and semimembranosus, and ends on the medial side of the crus; a tarsal tendon joins it to the common calcanean tendon.
Origin
- Vertebral head: first caudal vertebrae, broad sacrotuberous ligament and caudal fascia.
- Pelvic head: ventral surface of the ischial tuberosity (tuber ischiadicum).
Insertion
Tibial crest and crural fascia and, through the tarsal tendon, the calcaneal tuber.
Action
Extends the hip, flexes the stifle and helps extend the hock. It contributes to propulsion.
Innervation
Sciatic nerve (n. ischiadicus), through the tibial nerve, and the caudal gluteal nerve for the vertebral head.
Clinical relevance
- Fibrotic myopathy mainly affects this muscle, near its musculotendinous junction: muscle tissue is replaced by fibrous and sometimes ossified tissue, felt as a firm band on the caudal thigh. At the end of the swing phase the limb is jerked caudally and the hoof slaps down. It is linked to trauma, intramuscular injections and strain in horses working cattle; it is treated by tenotomy or myotomy.
- Together with the semimembranosus it is a site for muscle biopsy and intramuscular injection.