2 3 o INFERIOR EXTREMITY 



Small Lateral Rotator Muscles of the Thigh. Under this 

 heading are included the piriformis, obturator internus, gemelli, 

 the obturator externus, and the quadratus femoris. They 

 are all inserted into or in the neighbourhood of the greater 

 trochanter of the femur, and they are applied to the posterior 

 surface of the capsule of the hip-joint. 



The piriformis arises within the pelvis from the three middle 

 pieces of the sacrum, and slightly from the upper margin 

 of the great sciatic notch of the hip bone. The sacral 

 origin cannot be seen at present, but the iliac origin should 

 be made out. After passing through the great sciatic 

 foramen, the muscle is directed distally, laterally, and 

 anteriorly. Its fleshy belly rapidly tapers and ends in a 

 rounded tendon, which crosses superficial to the common 

 tendon of the obturator internus and gemelli, and is inserted 

 into a small impression on the highest part of the greater tro- 

 chanter of the femur (Fig. 75, p. 202). It is closely adherent 

 to the subjacent obturator tendon for some distance. The 

 piriformis is supplied by branches from the first and second 

 sacral nerves. 



The obturator internus and gemelli constitute, together, a 

 tricipital muscle with one large intra-pelvic belly (obturator 

 internus), and two small extra-pelvic bellies (gemellus superior 

 and inferior). The common tendon of this tricipital muscle 

 is inserted into an impression on the upper part of the greater 

 trochanter of the femur immediately anterior and medial to 

 the insertion of the piriformis (Fig. 75, p. 202). 



The gemellus superior arises from the spine of the ischium 

 at the upper margin of the small sciatic notch. Its fibres 

 pass laterally along the superior border of the tendon of the 

 obturator internus, and are inserted obliquely into that tendon. 

 The gemellus inferior arises from the tuberosity of the ischium, 

 at the lower margin of the small sciatic notch, and is in- 

 serted into the distal border of the obturator tendon, in 

 a similar manner to the gemellus superior. Close to their 

 origins the gemelli meet under cover of the obturator tendon, 

 and form a fleshy bed, on which it lies ; near the trochanter 

 the fibres of the gemelli overlap the obturator tendon, and 

 tend to cover its superficial surface. 



The tendon of the obturator internus should be freed from the 

 gemelli for some little distance from its point of exit from 

 the small sciatic foramen. It may then be divided and 



