418 THE INFERIOR EXTREMITY 



iliac spine to the ischial tuberosity at the junction of its lower 

 and middle thirds. 



The Sciatic Nerve (L. 4, 5, S. i, 2, 3) emerges below the 

 piriformis and passes distally, lying successively on the ischium, 

 the obturator internus and gemelli, and the quadratus femoris. 

 At the lower border of the quadratus it passes on to the posterior 

 surface of the adductor magnus, and is crossed superficially by 

 the long head of the biceps femoris ; which is running distally 

 and laterally (Fig. 123). 



In intractable cases of sciatica the nerve may be stretched 

 by open operation. The incision is carried vertically along the 

 thigh,, from the mid-point of the line joining the ischial tuber- 

 osity to the greater trochanter. After division of the skin and 

 fasciae, the lower border of the glutseus maximus and the biceps 

 tendon, which runs distally and laterally, are exposed. The 

 finger is passed into the angle between the two in a medial 

 direction, and the nerve is hooked up from under cover of the 

 biceps. 



The Inferior Gluteal (Sciatic) Artery appears at the lower 

 border of the piriformis and at once breaks up into numerous 

 branches. It can be exposed by the incision already described 

 for the ligature of the internal pudendal artery (p. 417). 



The crucial anastomosis occurs in the region of the quadrate 

 tubercle. Branches of the inferior and superior gluteal arteries, 

 which both arise from the hypogastric (internal iliac), anastomose 

 with branches of the medial and lateral circumflex arteries and 

 the first perforating, which arise from the profunda femoris. 

 In this way an important connection is formed between the 

 external iliac and the hypogastric trunks, and it is capable of 

 re-establishing the circulation in the lower limb, when the 

 external iliac is ligatured or when the femoral artery is tied 

 proximal to the origin of its profunda branch (p. 407). 



The Posterior Cutaneous (Small Sciatic) Nerve of the 

 thigh (S. i, 2, and 3) runs distally, under cover of the glutseus 

 maximus and on the surface of the sciatic nerve. At the lower 

 border of the maximus the nerve crosses the biceps superficially, 

 and continues its course through the thigh immediately under 

 the deep fascia and in the middle line of the limb. It gives off 

 twigs to supply the skin of the buttock and of the posterior 

 and medial aspects of the thigh (Fig. 124). 



Hernias may escape from the pelvis through the greater 

 sciatic foramen and appear at the upper or lower border of the 



