226 OBTURATOR INTERNUS AND EXTERNUS. 



the obturator foramen, and to the obturator membrane. It passes 

 out of the pelvis through the lesser sacro-ischiatic foramen, and is 

 inserted by a flattened tendon into the trochanteric fossa of the femur. 

 The lesser sacro-ischiatic notch, over which this muscle plays as 

 through a pulley, is faced with cartilage, and provided w 7 ith a 

 synovial bursa to facilitate its movements. The tendon of the 

 obturator is supported on each side by the two gemelli muscles 

 (hence their names), which are inserted into the sides of the tendon, 

 and appear to be auxiliaries or superadded portions of the obturator 

 internus. 



Relations. By its superficial or posterior surface with the internal 

 pudic vessels and nerve, the obturator fascia", which separates it from 

 the levator ani and viscera of the pelvis, the sacro-ischiatic liga- 

 ments, gluteus maximus, and ischiatic vessels and nerves. By its 

 deep or anterior surface with the obturator membrane and the 

 margin of bone surrounding it, the cartilaginous pulley of the lesser 

 ischiatic foramen, the external surface of the pelvis, and the capsular 

 ligament of the hip-joint. By its upper border, within the pelvis, 

 with the obturator vessels and nerve ; external to the pelvis, with 

 the gemellus superior. By its lower border with the gemellus inferior. 



The Gemellus inferior arises from the posterior point of the tube- 

 rosity of the ischium, and is inserted into the lower border of the ten- 

 don of the obturator internus, and into the trochanteric fossa of the 

 femur. 



Relations. By its superficial surface with the gluteus maximus, 

 and ischiatic vessels and nerves. By its deep surface with the ex- 

 ternal surface of the pelvis and capsule of the hip-joint. By its 

 upper 'border with the tendon of the obturator internus. By its 

 lower border with the tendon of the obturat<fr externus and quadratus 

 femoris. 



In this region the tendon only of the obturator externus can be 

 seen, situated deeply between the gemellus inferior and the upper 

 border of the quadratus femoris. To expose this muscle fully, it is 

 necessary to dissect it from the anterior part of the thigh, after the 

 removal of the pectineus and adductor longus and brevis muscles. 



The Obturator externus muscle (obturare, to stop up) arises from 

 the obturator membrane, and from the surface of bone immediately 

 surrounding it, viz. from the body and ramus of the os pubis and 

 ischium : its tendon passes behind the neck of the femur, to be in- 

 serted with the external rotator muscles, into the trochanteric fossa 

 of the femur. 



Relations. By its superficial or anterior surface with the tendon 

 of the psoas and iliacus, pectineus, adductor brevis and magnus, the 

 obturator vessels and nerve. By its deep or posterior surface with 

 the obturator membrane and the margin of bone which surrounds 

 it, the lower part of the capsule of the hip-joint and the quadratus 

 femoris. 



The Quadratus femoris (square-shaped) arises from the external 

 border of the tuberosity of the ischium, and is inserted into a rough 



