CUTANEOUS NERVES OVER GLTJTEUS. 581 



SECTION II. 



THE BUTTOCK, OR THE GLUTEAL REGION. 



Directions. Both this Section and the following one are to be completed 

 by the student in the time appointed for the body to lie in the prone 

 position. 



Position. During the dissection of the back of the thigh the body is 

 placed with the face down ; arid the pelvis is to be raised by blocks, until 

 the lower limbs hang almost vertically over the end of the dissecting table. 

 When the body is turned, the points of bone marking posteriorly the 

 limit between the thigh and the abdomen can be better ascertained. 



Dissection. The integument is to be raised from the buttock by means 

 of the following incisions : One is to be made along the iliac crest of the 

 hip bone, and is to be continued in the middle line of the sacrum to the 

 tip of the coccyx. Another is to be begun where the first terminates, and 

 is to be carried outwards across the thigh till it is about six inches below 

 the great trochanter. The flap of skin thus marked out is to be thrown 

 down. 



Many of the cutaneous nerves of this region will be found in the fat 

 along the line of the iliac crest. Thus in front, but rather below the crest, 

 are branches of the external cutaneous, if these have not been cut in the 

 dissection of the thigh. Crossing the crest towards the fore part is a large 

 offset of the last dorsal nerve ; and usually farther back, but close to the 

 bone, a smaller branch from the ilio-hypogastric nerve. In a line with 

 the outer border of the erector spince, are two or three branches of the 

 lumbar nerves. 



By the side of the sarcum and coccyx two or three offsets of the sacral 

 nerves are to be looked for beneath the fat. 



The remaining cutaneous nerves are derived from the small sciatic, and 

 must be sought beneath the fat along the line of the lower incision, where 

 they come from underneath the gluteus maximus. A few turn upwards 

 over that muscle ; the rest are directed down the thigh, and one (inferior 

 piidendal) bends below the ischial tuberosity to reach the perinceal space. 



Cutaneous arteries accompany all the nerves, and will serve as guides 

 to their situation. 



CUTANEOUS NERVES (fig. 199). The nerves distributed in the integu- 

 ments of the buttock are small but numerous, and are derived from the 

 spinal nerves (posterior primary pieces) ; from branches of the lumbar and 

 sacral plexuses ; and from the last dorsal nerve. 



Branches of the lumbar nerves ( 6 ). The offsets of the posterior primary 

 pieces of the lumbar nerves (p. 367) are two or three in number, and cross 

 the crest of the hip bone near the anterior edge of the erector spinae : they 

 ramify in the integuments of the middle of the buttock, and some branches 

 may be traced nearly to the trochanter major. 



The branches of the sacral nerves ( 5 ) perforate the gluteus maximus 

 near the sacrum and coccyx, and are then directed outwards for a short 

 distance in the integuments over the muscle. These offsets are usually 

 two in number : the largest is opposite the lower end of the sacrum, and 

 the other by the side of the coccyx. 



The last dorsal nerve ( 8 ) supplies the buttock by means of its lateral 



