4i6 THE INFERIOR EXTREMITY 



part of the incision lies distal to the greater trochanter. Free 

 exposure is necessary, as the bursae when diseased may possess 

 extensive prolongations. 



The glutaeus maximus covers most of the dorsum ilii and 

 the muscles, to which it gives origin, and both the sacro-tuberous 

 and the sacro-spinous (greater and lesser sacro-sciatic) ligaments. 

 In addition, it covers both the greater and lesser sciatic foramina 

 and the vessels and nerves which they transmit (Fig. 123). 



The Piriformis (p. 355) emerges from the greater sciatic foramen, and, 

 as it passes laterally to the apex of the greater trochanter, it lies on the postero- 

 superior aspect of the capsule of the hip-joint. It abducts the thigh, and 

 receives its nerve-supply from S. i and 2. 



The Glutaeus Medius is exposed above the upper border of the maximus, 

 but its posterior part is covered over by that muscle. It arises from the dorsum 

 ilii, and is inserted into an oblique ridge which runs forwards and distally 

 across the lateral aspect of the greater trochanter. The lower or posterior 

 border of the medius lies along the upper border of the piriformis. 



The Glutaeus Minimus arises from the dorsum ilii, under cover of the 

 medius. As it passes to its insertion on the anterior aspect of the greater 

 trochanter, the muscle is closely related to the superior aspect of the capsule 

 of the hip-joint. 



Both the glutaeus medius and minimus act as powerful abductors of the 

 thigh, but, in addition, their anterior fibres, which lie deep to the tensor 

 fasciae latas, assist in medial rotation. The nerve-supply to both muscles is 

 derived from the superior gluteal (L. 4 and 5, S. i). 



The Superior Gluteal Artery, a branch of the hypogastric 

 (p. 369), enters the buttock through the greater sciatic foramen 

 between the adjoining borders of the piriformis and the glutseus 

 medius. It possesses a short trunk, which divides into a super- 

 ficial and a deep division. The former enters the maximus and 

 the latter breaks up into upper and lower branches, which pass 

 laterally between the medius and the minimus. 



The upper branch terminates in the region of the anterior 

 superior iliac spine, where it anastomoses with the superficial 

 and deep circumflex iliac arteries (p. 253) and the ascending 

 branch of the lateral circumflex. This anastomosis constitutes 

 a connection between the hypogastric (internal iliac) and the 

 external iliac trunks (p. 408). 



The superior gluteal artery may require to be ligated either 

 for aneurism or following stab wounds in the buttock. The 

 incision is made parallel to the fibres of the glutseus maximus, 

 and its centre lies at the junction of the upper and middle thirds 

 of the line joining the posterior superior iliac spine to the greater 

 trochanter. Owing to the depth at which the vessel lies and 

 the shortness of its main trunk, the incision should be a fairly 

 large one. 



