584 DISSECTION OF THE BUTTOCK. 



which the lower fibres are closely joined. The depth of the muscle will 

 be ascertained by the fascia and some vessels beneath it. When this in- 

 termuscular layer is arrived at, the outer part of the gluteus is to be 

 thrown towards its insertion, and the sciatic artery and nerves are to be 

 detached from the under surface, though the branches of the gluteal ves- 

 sels entering the muscle must be cut. 



The loose fat is to be taken away from the hollow between the pelvis 

 and the trochanter, without injuring the vessels and nerves ; and the 

 several muscles are to be cleaned, the fibres of each being made tense at 

 the time of its dissection by rotating the femur. The vessels, nerves, and 

 muscles, which are to be defined, may be ascertained by referring to the 

 enumeration below of the parts beneath the gluteus. In removing the 

 areolar tissue from the ischial tuberosity and the great trochanter, the 

 bursa'on each prominence of bone will be observed. 



Lastly the origin of the muscle is to be removed ; and the sacral nerves 

 a"re to be dissected out of the gluteus, and to be followed to the surface of 

 the great sacro-sciatic ligament, where they will be afterwards seen. 



Parts beneath the gluteus (fig. 200). At its origin the gluteus maximus 

 i^ests on the pelvis, and conceals part of the hip bone, sacrum, and coccyx, 

 also the ischial tuberosity with the origin of the hamstring muscles, L, 

 and the great sacro-sciatic ligament, K. At its insertion it covers the 

 upper end of the femur, with the great trochanter, and the origin of the 

 vastus externus,. i. Between the muscle and each prominence of bone, 

 viz. the tuberosity and the trochanter, is a large, loose synovial membrane ; 

 and between it and the vastus externus is another synovial sac. 



In the hollow between the pelvis and the femur the muscle conceals, 

 from above downwards, the undermentioned parts : First, a portion of 

 the gluteus medius, A ; and below it the pyriformis, B, with the superficial 

 branch (a) of the gluteal vessels between the two. Coming from beneath 

 the pyriformis are the sciatic vessels (>), and the large and small sciatic 

 nerves ( 3 , ), which descend to the thigh between the great trochanter and 

 the ischial tuberosity ; and internal to the sciatic are the pudic vessels and 

 nerve (d, 5 ), and the nerve to the obturator internus muscle ( 4 ) witli its 

 vessels, which are directed inwards through the small sacro sciatic notch. 

 Still lower down is the tendon of the obturator internus muscle, D, with a 

 fleshy fasciculus the gemellus (c and K) above and below it. Next 

 comes the thin quadratus femoris muscle, G, with the upper part of the 

 adductor magnus, n : at the upper border of the quadratus is the tendon 

 of the obturator externus, F ; and at the lower border, between it and the 

 adductor, issues one of the terminal branches of the internal circumflex 

 artery (c) with its veins. 



Dissection. Tracing back the offsets of the sacral nerves which perfo- 

 rate the gluteus, and removing a fibrous stratum which covers them, the 

 looped arrangement of the first three nerves on the great sacro-sciatic 

 ligament will appear. Finally the nerves may be followed inwards beneath 

 the multifidus spinse to the posterior sacral foramina. 



Sacral nerves. The external pieces of the posterior primary branches 

 of the first three sacral nerves, after passing outwards beneath the multi- 

 fidus spinas (p. 372), are joined by loops on the surface of the great sacro- 

 sciatic ligament (fig. 120). 



Two or three cutaneous offsets are derived from this intercommunica- 

 tion, and pierce the fibres of the gluteus maximus to be distributed on the 

 surface (p. 581). 



