310 Anatomy Applied to Medicine and Surge? y. 



Pyriformis. From the anterior surface of the sacrum, 

 between the first, second, third and fourth foramina ; from 

 the anterior surface of the sacro-sciatic ligament and from 

 the margin of the great sacro-sciatic foramen; into the 

 inner surface of the anterior portion of the upper border 

 of the great trochanter. Action. It rotates the thigh 

 outwards, and, acting from below, rotates the pelvis to- 

 wards the opposite side. 



Obturator Intermix. From the inner surface of the 

 obturator membrane and a portion of the bony ring sur- 

 rounding the foramen ; into the inner surface of the upper 

 border of the great trochanter near the neck of the femur. 

 Action. It rotates the thigh outwards. 



Gemellus Superior and Inferior. The former from the 

 outer surface of the spine of the ischium ; into the upper 

 border of the tendon of the obturator internus about one 

 inch from its insertion ; the latter, from the upper part of 

 the inner border of the tuberosity; into the lower border 

 of the above tendon, the same distance from its insertion 

 as the gemellus superior. The action of these muscles is 

 similar to that of the obturator internus. 



Quadratus Femoris. From the upper part of the outer 

 border of the tuberosity of the ischium; into the linea 

 quadrata of the femur. Action. External rotation of the 

 thigh. 



These muscles, rotators in action, are all supplied by 

 the same nerves, viz., the lumbo-sacral, and branches from 

 the first and second sacral nerves the gluteus maximus 

 receiving, in addition, fibres from the third sacral, through 

 the inferior gluteal nerve. 



On removal of the gluteus maximus the following 

 structures are exposed, from above downwards : The pos- 

 terior portions of the gluteus medius and gluteus minimus 

 muscles ; the gluteal artery and its branches ; the superior 



