292 THE INFERIOR EXTREMITY 



vessels, the pudendal nerve, the nerve to the obturator 

 interims and superior gemellus, and the nerve to the 

 quadratus femoris and inferior gemellus. Through the lesser 

 sciatic foramen pass the obturator internus muscle, the 

 pudendal nerve, the nerve to the obturator internus and 

 the internal pudendal vessels (Fig. 129). All the structures 

 mentioned, as well as other muscles, vessels, and nerves, have 

 to be cleaned and examined. Therefore the second day's 

 dissection is extensive and complicated, and unless it is 

 proceeded with in a regular and definite manner it will not 

 be successfully completed. 



Dissection. Commence with the superficial branches of the 

 superior gluteal artery, which enter the upper part of the deep 

 surface of the glutasus maximus, and follow them to the point 

 where they emerge through the cleft between the border of the 

 glutaeus medius and the upper border of the adjacent piriformis 

 muscle. Then clean the piriformis, from the great sciatic 

 foramen, through which it emerges, to the greater trochanter, 

 where its tendon disappears under cover of the glutseus medius. 

 After the piriformis is defined, clean the posterior cutaneous 

 nerve of the thigh, following it upward to its exit from the 

 greater sciatic foramen at the lower border of the piriformis. 

 Secure its perineal branch, which springs from its medial 

 border and passes forwards and medially towards the perineum, 

 anterior to the tuber ischii, and note the cutaneous branches 

 which were seen on the lower part of the glutaeus maximus. 

 The posterior cutaneous nerve is sometimes accompanied by a 

 branch of the inferior gluteal artery. If the inferior gluteal 

 vessels and nerve, which lie medial to the posterior cutaneous 

 nerve, were not displayed as the glutaeus maximus was reflected, 

 clean them now, and follow them to the lower border of the 

 piriformis. When the inferior gluteal artery and its branches 

 have been cleaned, place the leg on a large block to flex the 

 knee, so that the structures in the buttock and the back of the 

 thigh may be relaxed, then proceed to secure and clean the 

 sciatic nerve. It is the large white firm cord which lies immedi- 

 ately deep to the posterior cutaneous nerve. Therefore pull the 

 latter nerve medially with hooks, then at the level of the top of 

 the trochanter major cut longitudinally through the fascia on 

 the sciatic nerve till the nerve is exposed. Insert the handle 

 of the scalpel into the incision in the fascia and run it upwards, 

 along the lateral border of the nerve, to the greater sciatic foramen 

 and downwards to the point where the nerve passes anterior to 

 the biceps femoris and leaves the area of the present dissection. 

 Clean the fascia from the back of the nerve from the lateral to 

 the medial border, and secure the branches to the hamstring 

 muscles, which spring from the medial border, at or a little 

 distal to the level of the tuber ischii. Follow the branches to 

 the muscles and preserve the branches of the medial femoral 

 circumflex artery which join the nerves as they approach their 

 terminations. 



