460 THE MUSCULATURE 



of origin and insertion, the other descends to enter the middle third of the distal deep portion 



Action.— It is the most powerful extensor of the thigh. It also serves slightly to rotate the 

 limb lateralward and to make tense the fascia lata, and through the iho-tibial band to keep the 

 extended knee-joint steady. When the thigh is extended the major part of the muscle is an 

 adductor but the upper part is a weak abductor. The whole muscle is an abductor when the 

 thigh is flexed. It is brought powerfully into play in cUmbing and in walking up hill. 



Fig. 408. — The Lateral Rotators and the Hamstring Muscles. 



Gluteus medius 



Piriformis 



Gemellus supenorj 



Gemellus inferior 

 Quadratus femons 



Gluteus maximus 



Vastus intermedius 



Short head of biceps 



Plantaris 



Gastrocnemius 



Semi-membranosus 



Sartorius 



Semi-tendinosus 



Relations.— It is covered by the fatty superficial tissue of the buttock. It extends over the 

 posterior portion of the ilium, the lateral surface of the sacrum and coccyx, the sacro-tuberous 

 ligament, and the great trochanter. It covers the tuber of the ischium in the standing but not 

 in the sitting position. Immediately beneath the mu.scle lie portions of the gluteus medius, 

 piriformis, obturator internus, gcmelli, quadratus femoris, obturator externus, and hamstring 

 muscles, and of the gluteal vchscIh and nerves and the sciatic nerve. 



Varinlions. — Few anomalies arc recorded. The deep distal portion of the muscle may be 

 more isolated than normal in the adult. A special coccygeo-femoral muscle may run from the 

 coccyx to the iinea aspera, or from the sacro-tuberous ligament to the fascia of the leg. A 



