THE THIGH 



1443 



skin of the buttock is coarse and difficult to cleanse satisfactorily. The abun- 

 dance of sebaceous glands accounts for the frequency of boils here. 



Gluteus maximus. — The 'fold of the buttock' neither corresponds accurately 

 to, nor is caused by, the lower margin of this muscle. Thus, medially, it lies below 

 the lower margin of the muscle, as it runs laterally it crosses it, and comes to lie 

 on the muscle. The fold is really due to creasing of the skin adherent here to the 

 coarsely fibro-fatty tissue over the tuber ischii during extension. But in early hip 

 disease, in which flexion of the joint is, with wasting of the muscle, almost unvary- 

 ingly present, the fold disappears with well-known rapidity. The prominence of 

 the buttock is mainly due to the gluteus maximus, especially behind and below, 

 and in less degree to the other two glutei in front. Under the lower edge of the 

 gluteus maximus the edge of the sacro-tuberous (great sacro-sciatic) ligament can 

 be felt on deep pressure. 



To mark out the upper border of the gluteus maximus a line is drawn from a point on the 

 iUac crest 5 cm. (2 in.) in front of the posterior superior spine, downward and laterally to the 

 back of the great trochanter. The lower border is marked out by a second Une drawn from the 

 side of the coccyx parallel with the former, and ending over the linea aspera at the junction of 

 the upper and middle thirds of the thigh. It must be remembered that only the lower and inter- 

 nal fibres of the muscle are inserted into the gluteal ridge on the femur. The greater part of 



Fig. 1161. — Section through the Hip and Gluteal Region. (One-third.) 



SartoriuE 

 Reflected tendon 



of rectus \, 

 Psoas and iliacus 

 and bursa \ 

 Femoral nerve v^ 



Common femoral.^ 

 artery 

 Common femoral vein.^^ 



Profunda vessels 



Gracilis^|T^p- 



Adductor brevis-^^J^-^ 

 Senii-tendinosus.'E^--V- 

 Obturator externus— / 

 Adductor magnus 

 Adductor longus- 



"Gluteus maximus 

 'Gluteus medius 



'Gluteus minimus 



■ Piriformis 



,Sciatic nerve and infe« 

 rior gluteal vessels 



"Obturator internus 

 "Gemelli 



"Biceps 



-Quadratus femoris 



it is inserted into the fascia lata and ilio-tibial band and so into the lateral condyle of the tibia. 

 Weakness of the gluteus maximus and tensor fasciae latae, with consequent laxity of the ilio- 

 tibial band, gives rise to abnormal side-to-side passive mobility at the knee-joint in full extension. 



Nerves and vessels. — The following superficial nerves can be marked in over 

 the buttock (fig. 1182). 



Behind the great trochanter, branches of the lateral cutaneous; coming down over the crest, 

 the lateral cutaneous branch of the last thoracic (about in a line with the great trochanter), 

 and behind this the lateral branch of the ilio-hypogastric. Two or three offsets of the posterior 

 primary branches of the lumbar nerves cross the hinder part of the iliac crest at the lateral 

 margin of the sacro-spinalis. Two or three twigs from the posterior divisions of the sacral 

 nerves pierce the gluteus maximus close to the coccyx and sacrum, and ramify laterally. Fi- 

 nally, over the lower border of the gluteus maximus, turn upward branches of the posterior 

 cutaneous (small sciatic) and its perineal branch (inferior pudendal), and the fourth sacral 

 nerve. 



Sciatic nerve (figs. 1162, 1163). — The point of emergence below the gluteus 

 maximus and the track of this nerve (fourth and fifth lumbar and first three sacral 

 nerves) will be given by a line drawn from a spot a little medial to the middle of 

 the space between the great trochanter and the tuber ischii to the lower part of 

 the back of the thigh, where it usually divides into the tibial and common peroneal 

 (internal and external popliteal) nerves. 



