PLATE XXV. 



THE BUTTOCK (GLUTEUS MAXIMUS). 



This dissection is to show the gluteus maximus : the superficial layer of the fascia 

 lata which covers it has been removed and cut short along the outer edgo of the muscle. 

 The cutaneous nerve supply of this region is indicated by the accompanying dia- 

 gram : (a) Gluteal recurrent branch of 

 the external cutaneous [2 and 8 Lj. 

 (a 1 ) Branches from the external cuta- 

 neous supplying the outer side of the 

 thigh, (b) Lateral branch of the last 

 dorsal nerve, (c) Iliac branch of 

 the ilio-hypogastric. Both these two 

 are derived from the anterior primary / 

 divisions of the spinal nerves, (d) Ex- 

 ternal branches of the posterior primary I 

 divisions of the first and second lumbar / ( 

 nerves, (e) External branches of the I \ 

 posterior divisions of the sacral nerves. I 

 (/) Perforating cutaneous nerve from / 

 the third and fourth anterior divisions / 

 of the sacral nerves, (g) Gluteal branches I 

 of the small sciatic, (h, i) Internal and I 

 external cutaneous branches of the small 

 sciatic to back of thigh, (k) Terminal 

 branch of small sciatic which pierces the fascia at the upper 

 part of the popliteal space, and supplies the skin as far as 

 middle of calf. (I) Inferior pudendal or nerve of Som- 

 mering. (m) Cutaneous branch of the obturator, (n) Pos- 

 terior branch of the internal cutaneous. 



The other side of the diagram shows Lizars's lines, which 

 are the guides for finding the position of the gluteal and 

 sciatic arteries at the point of their -emergence from the 

 pelvis. For the gluteal, bisect the line A B drawn between 

 the tuber ischii and great trochanter at C, and draw a line 

 from this point to the posterior superior spine of the ilium ; 

 trisect this line C E, and the upper point of trisection will be 

 about the point at which the artery emerges. For the sciatic 

 trisect the line A B and join the inner trisection with the posterior superior spine ; 

 this line bisected will indicate about the spot where it emerges from the pelvis. 



Nor should Nelaton's line be forgotten, as it is important clinically : it is marked 

 out by joining the anterior superior iliac spine with the anterior part of the tuber ischii ; 

 it just crosses the top of the great trochantor, and affords a ready means of recognising 

 displacements from dislocations or fractures pf the neck of the femur. 



The fold of the buttock has nothing to do with the edge of the gluteus maximus ; 

 it is below the edge of the muscle at the inner part of the thigh, crossing it externally, 

 and being best marked just below the ischial tuberosity. It is due to the relaxation of 

 the skin in the erect position, and is lost when the thigh is flexed.' 



The subcutaneous tissue of this region in many of the negro races is an extremely 

 thick layer, forming a regular pad or cushion. 



The large size of the gluteus maximus is characteristic of man, its chief use being 

 to extend the thigh, and thus maintain the body in the erect position ; even in the 

 anthropoid apes it is not nearly so well developed, and is less again in mammals. The 

 part arising from the coccyx and sacrum may be separated, thus representing the 

 agitator cauchc of animals. 



It has the coarsest fascicles of any muscle in the body. 



1 Dr. Symington, Journal of Aiiatomy and Physiology, vol. xviii. p. 198. 



