Overview
It covers much of the lateral thigh, caudal to the femur. Unlike in ruminants, in the horse it is not fused with the superficial gluteal. It has two heads of origin: a vertebral head, which climbs to the sacrum and tail base and gives the croup its rounded outline, and a pelvic head from the ischial tuberosity. Distally it splits into several branches that end in a broad aponeurosis.
Origin
- Vertebral head: spinous processes of the sacrum, broad sacrotuberous ligament, and gluteal and caudal fasciae.
- Pelvic head: ischial tuberosity (tuber ischiadicum).
Insertion
Through an aponeurosis continuous with the fascia lata and crural fascia:
- Cranial branch: patella and lateral patellar ligament.
- Middle branch: tibial crest.
- Caudal branch: crural fascia and, through a tarsal tendon, the calcaneal tuber, as part of the common calcanean tendon.
Action
Extends the hip and abducts the limb. The cranial branch extends the stifle and the caudal branches flex it; the tarsal tendon helps extend the hock. It is one of the main drivers of propulsion.
Innervation
Caudal gluteal nerve (n. gluteus caudalis) for the vertebral head and branches of the sciatic nerve (n. ischiadicus).
Clinical relevance
- The caudal thigh muscles are a common intramuscular injection site in the horse, especially in foals. The sciatic nerve runs deep to this muscle, so the needle is aimed into the muscle mass and not towards the femur.
- In exertional rhabdomyolysis ("tying-up") the large muscles of the croup and thigh become hard and painful; the horse is reluctant to move and creatine kinase activity rises.