1180 



SURGICAL AND TOPOGRAPHICAL ANATOMY 



THE BUTTOCKS 



Bony landmarks. — The finger readily traces the whole oiitlme of the iliac 

 crest. Behind, it terminates in the posterior superior spine, which corresponds in 

 level to the second sacral spine and the centre of the sacro-iliac joint (Holden). 



The third sacral sjnne marks the lowest limit of the spinal membranes and the 

 cerebro-spinal Huid; it also corresponds to the upper border of the great sacro- 

 sciatic notch. 



The first piece of the coccyx corresponds to the spine of the ischium (Windle). 

 Its apex is in the furrow just behind the last piece of the rectum. 



Fig. 746.— Positiox and Direction of the Superficial, In'cisioxs which must be 



MADE IN order TO REACH THE GLUTEAL, SCIATIC, AND PUDIC ARTERIES. 



A.B. Ilio-trochanteric line divided into thirds, and corresponding in direction with the line of the 

 gluteus maxinius. The incision to reach the gluteus niaximus is indicated by the dark part of the 

 line. Its centre is at the jjositiou of the upper' and middle thirds of the ilio-trochauteric line, and 

 corresponds with the point of emergence of the artery from the great sciatic notch. 



A.C. Ilio-ischiatic line. The incision to reach the sciatic or pudic artery is indicated by the lower 

 dark line. This is also to be made in the direction of the fibre of the gluteus maximus. Its centre 

 corresponds to the position of the loAver and middle thirds of the ilio-ischiatic line. 



ANTERIOR SUPEHIOR ILIAC SPINE (» 



GREAT TROCHANTER (Bj 



.1) POSTERIOR SUPERIOR ILIAC SPINE 



(Cj TUBEROSITY OF ISCHIUM 



The tuberosities of the ischium are readily felt by deep pressure on either side 

 of the anus. In the erect position they are covered by the lower margin of the 

 gluteus maximus. In sitting they are protected by tough skin, fascia?, with coarse 

 fibrous fat, and often by a bursa known, according to the patients in whom it 

 becomes enlarged, as 'weaver's, coachman's, lighterman's, drayman's' bursa. 



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

 to, nor is caused by, the lower margin of this muscle. It 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 tlie joint is almost 

 unvaryingly present, both the fold and the gluteus maximus disappear with char- 

 acteristic rapidity. The prominence of the luittock is mainly due to the gluteus 



