298 THE INFERIOR EXTREMITY 



Nervus Ischiadicus (O.T. Great Sciatic Nerve). The sciatic 

 nerve, the largest nerve in the body, comes from the sacral 

 plexus, and enters the gluteal region through the lower part 

 of the great sciatic foramen. At first it has the form of a 

 flattened band, but soon it becomes oval or round, as seen in 

 section. Covered by the glutaeus maximus, the sciatic nerve 

 traverses the gluteal region in the interval between the greater 

 trochanter of the femur and the tuberosity of the ischium. 

 From above downwards it lies on the body of the ischium 

 and the nerve to the quadratus femoris, the tendon of the 

 obturator internus with the two gemelli muscles, the quadratus 

 femoris, and the adductor magnus. The nerves to one or 

 more of the hamstring muscles issue from the main trunk 

 near the lower border of the glutaeus maximus. 



The sciatic nerve frequently escapes from the pelvis in the form of two 

 trunks (the two divisions into which it normally divides in the thigh, viz., 

 the tibial and the common peroneal) which enclose between them a portion 

 of the piriformis muscle. 



Arteria Pudenda Interna, Nervus Pudendus (O.T. Internal 

 Pudic), and the Nerve to the Obturator Internus. The 

 internal pudendal artery, the pudendal nerve and the nerve 

 to the obturator internus muscle are exposed, in the present 

 dissection, only in a very short part of their extent. They all 

 emerge from the greater sciatic foramen and cross the spine 

 of the ischium or the adjacent part of the sacro-spinous 

 ligament ; then they enter the lesser sciatic foramen and pass 

 out of view. The nerve to the obturator internus is placed 

 most laterally. It lies on the base of the ischial spine, and 

 furnishes a twig to the gemellus superior. The internal 

 pudendal artery -, with a companion vein on each side, crosses 

 the tip of the spine. The pudendal nerve is placed most 

 medially, and lies on the sacro-spinous ligament, close to its 

 attachment to the spine. In some cases, however, the 

 pudendal" nerve unites in a plexiform manner with the 

 nerve to the obturator internus, so that the whole, or a part, 

 of it may lie lateral to the pudendal vessels. 



Small Lateral Rotator Muscles of the Thigh. Under this 

 heading are included the piriformis, the obturator internus, 

 and the two gemelli, the quadratus femoris, and the obturator 

 externus. They all lie directly under cover of the glutaeus 

 maximus in the greater part of their extent, except the 

 obturator externus which lies deep (anterior) to the quadratus 



