516 THE MUSCLES AND FASCIA. 



This muscle should now be divided near its insertion and turned upward, when the Gluteus 

 minimus will be exposed. 



The G-luteus minimus, the smallest of the three Glutei, is placed immediately 

 beneath the preceding. It is fan-shaped, arising from the outer surface of the 

 ilium, between the middle and inferior gluteal lines, and behind, from the margin 

 of the great sacro-sciatic notch ; the fibres converge to the deep surface of a 

 radiated aponeurosis, which, terminating in a tendon, is inserted into an impres- 

 sion on the anterior border of the great trochanter. A synovial bursa is inter- 

 posed between the tendon and the great trochanter. 



Relations. By its superficial surface, with the Gluteus medius, and the gluteal 

 vessels and superior gluteal nerve ; by its deep surface, with the ilium, the reflected 

 tendon of the Rectus femoris, and capsular ligament of the hip-joint. Its anterior 

 margin is blended with the Gluteus medius; its posterior margin is often joined 

 with the tendon of the Pyriformis. 



The Pyriformis is a flat muscle, pyramidal in shape, lying almost parallel with 

 the posterior margin of the Gluteus medius. It is situated partly within the pelvis 

 at its posterior part and partly at the back of the hip-joint. It arises from the 

 front of the sacrum by three fleshy digitations attached to the portions of bone 

 between the first, second, third, and fourth anterior sacral foramina, and also from 

 the groove leading from the foramina : a few fibres also arise from the margin of 

 the great sacro-sciatic foramen and from the anterior surface of the great sacro- 

 sciatic ligament. The muscle passes out of the pelvis through the great sacro- 

 sciatic foramen, the upper part of which it fills, and is inserted by a rounded 

 tendon into the upper border of the great trochanter, behind, but often blended 

 with, the tendon of the Obturator internus and Gemelli muscles. 



Relations. By its anterior surface, within the pelvis, with the Rectum (espe- 

 cially on the left side), the sacral plexus of nerves, and the branches of the internal 

 iliac vessels ; external to the pelvis, with the os innoniinatum and capsular liga- 

 ment of the hip-joint; by its posterior surface, within the pelvis, with the sacrum, 

 and external to it, with the Gluteus maximus; by its upper border, with the 

 Gluteus medius, from which it is separated by the gluteal vessels and superior 

 gluteal nerve ; by its lower border, with the Gemellus superior and Coccygeus, 

 the sciatic vessels and nerves, the internal pudic vessels and nerve, and muscular 

 branches from the sacral plexus, passing from the pelvis in the interval between the 

 two muscles. 



The Obturator membrane is a thin layer of interlacing fibres which closes the 

 obturator foramen. It is attached, externally, to the margin of the foramen ; 

 internally, to the posterior surface of the ischio-pubic ramus, internal to the inner 

 margin of the foramen. It is occasionally incomplete, and presents at its upper 

 and outer part a small canal, which is bounded below by a thickened band of fibres, 

 for the passage of the obturator vessels and nerve. Each obturator muscle is 

 connected with this membrane. 



Dissection. The next muscle, as well as the origin of the Pyriformis, can only be seen 

 when the pelvis is divided and the viscera removed. 



The Obturator internus, like the preceding muscle, is situated partly within 

 the cavity of the pelvis and partly at the back of the hip-joint. It arises from the 

 inner surface of the anterior and external wall of the pelvis, around the inner side 

 of the obturator foramen, being attached to the descending ramus of the os pubis 

 and the ascending ramus of the ischium, and at the side to the inner surface of 

 the body of the ischium, between the margin of the obturator foramen in front 

 and the great sacro-sciatic notch behind, and to the inner surface of the ilium 

 below the brim of the true pelvis. It also arises from the inner surface of the 

 obturator membrane, except at its lower part, and from the tendinous arch which 

 completes the canal for the passage of the obturator vessels and nerve. The fibres 

 are directed backward and downward, and terminate in four or five tendinous 

 bands which are found on its deep surface : these bands are reflected at a right 



