GLUT^AL REGION 229 



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

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

 plexus, and enters the glutaeal 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 glutaeal region in the interval between the great 

 trochanter of the femur and the tuber ischiadicum. Proximo- 

 distally it lies on the innominate bone (at the lower margin of 

 the great sciatic notch), the tendon of the obturator internus 

 with the two gemelli muscles, the quadratus femoris, and the 

 adductor magnus. In this region it does not, as a rule, 

 give off any branch, but occasionally the nerves to one or 

 more of the hamstring muscles issue from the main trunk as 

 high as the level of the quadratus femoris. 



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

 trunks (the two divisions into which it divides lower down, viz. the tibial 

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

 piriformis muscle. 



Dissection. The student should flex the knee and raise it on a block in 

 order to relax the sciatic nerve. By pulling this great nerve-trunk laterally, 

 the dissector will expose the nerve to the quadratus femoris lying directly 

 upon the hip bone. Medial to this he will find the pudendal vessels 

 and nerve with the nerve to the obturator internus crossing the spine 

 of the ischium. These structures require to be carefully cleaned. The 

 twig from the nerve to the obturator internus to the gemellus superior 

 is especially liable to injury. The dissection will be improved by scraping 

 off the periosteum from the small area of bone which is in relation to the 

 above-mentioned vessels and nerves. 



Internal Pudendal Vessels and Pudendal Nerve (O.T. 

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



These structures emerge from the great sciatic foramen, below 

 the piriformis, and are only exposed in the present dis- 

 section for a very short part of their course. They pass out 

 of view by entering the small sciatic foramen. 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 ligamentum 

 sacro-spinosum 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. 

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