Overview
It lies medial to the semitendinosus and forms the medial part of the caudal thigh. In the horse, besides the pelvic head, it has a small vertebral head that climbs towards the tail base and adds to the rounded outline of the buttock.
Origin
- Vertebral head: caudal border of the broad sacrotuberous ligament and caudal fascia.
- Pelvic head: ventral surface of the ischial tuberosity (tuber ischiadicum).
Insertion
Medial epicondyle of the femur.
Action
Extends the hip and adducts the limb.
Innervation
Sciatic nerve (n. ischiadicus), through the tibial nerve.
Clinical relevance
- Together with the semitendinosus it is the usual site for muscle biopsy in the diagnosis of polysaccharide storage myopathy (PSSM) and other equine myopathies.
- The caudal thigh muscles are used for intramuscular injections, especially in foals. An abscess here drains distally more easily than one in the croup.
- Fibrotic myopathy can involve it together with the semitendinosus.