THE GLUTEAL REGION. 



431 



second sacral nerves through the inferior gluteal nerve from the sacral plexus ; 

 the Gluteus medius and minimus, by the fourth and fifth lumbar and first sacral 

 nerves through the superior gluteal ; the Pyriformis is supplied by the first and 

 second sacral nerves; the Gemellus inferior and Quadratus femoris by the last 

 lumbar and first sacral nerve ; the Gemellus superior and Obturator internus by 

 the fifth lumbar and first and second sacral nerves, and the Obturator externus by 

 the second, third, and fourth lumbar nerves through the obturator. 



Obturator 

 ^ artery. 



Anterior division of 

 obturator nerve. 



Anterior inferior 

 iliac spine. 



Capsular liga- 

 ment partly 

 cut away. 



Posterior division 

 of obturator 

 nerve. 



Internal circum-\ 

 flex artery. 



FIG. 257. Obturator externus muscle. (From a preparation in the Museum of the Royal College of Surgeons of 



England.) 



Actions. The Gluteus maximus, when it takes its fixed point from the pelvis, 

 extends the femur and brings the bent thigh into a line with the body. Taking 

 its fixed point from below, it acts upon the pelvis, supporting it and the whole 

 trunk upon the head of the femur, which is especially obvious in standing on one 

 leg. Its most powerful action is to cause the body to regain the erect position 

 after stooping by drawing the pelvis backward, being assisted in this action by 

 the Biceps, Semitendinosus, and Semimembranosus. The Gluteus maximus is a 

 tensor of the fascia lata, and by its connection with the ilio-tibial band it steadies 

 the femur on the articular surface of the tibia during standing, when the extensor 

 muscles are relaxed. The lower part of the muscle also acts as an adductor and 

 external rotator of the limb. The Gluteus medius and minimus abduct the 

 thigh when the limb is extended, and are principally called into action in 

 supporting the body on one limb, in conjunction with the Tensor fasciae femoris. 

 Their anterior fibres, by drawing the great trochanter forward, rotate the thigh 

 inward, in which action they are also assisted by the Tensor fasciae femoris. The 

 remaining muscles are powerful rotators of the thigh outward. In the sitting 

 posture, when the thigh is flexed upon the pelvis, their action as rotator ceases, and 

 they become abductors, with the exception of the Obturator externus, which still 

 rotates the femur outward. When the femur is fixed, the Pyriformis and Obturator 

 muscles serve to draw the pelvis forward if it has been inclined backward, and 

 assist in steadying it upon the head of the femur. 



