THE MUSCLES OF THE BUTTOCK. 



415 



M. Glutaeus Maximus. The glutaeus maximus is a large quadrilateral muscle, 



i with a crescentic origin. It arises from, (1) a portion of the area on the dorsum 



ilii above the posterior gluteal line (Fig. 369); (2) the tendon of the sacro- 



I spinalis muscle ; (3) the dorsal surface of the sacrum and coccyx (Fig. 395, 



p. 443); and (4) the posterior surface of the sacro-tuberous ligament. The fibres 



which form its superior and lateral border take origin directly from the fascia lata 



which envelops the muscle. 



The muscle forms a large fleshy mass, whose fibres are directed obliquely over 

 the buttock, invested by the fascia lata, and are inserted, by short tendinous fibres, 

 partly into the fascia lata over the greater trochanter of the femur (joining the 

 ilio-tibial tract), and partly into the gluteal tuberosity (Fig. 3*70, p. 416). The 

 fascia lata receives the insertion of the whole of the superficial fibres of the muscle 

 j and the superior half of the deep fibres. The inferior half of the deep portion of 



Obliquus externus abdominis 

 (insertion) 



Glutseus maximus 

 (origin) 



Tensor fasciae latse 

 (origin) 



Sartorius (origin) 



Rectus femoris (reflected^head 

 of origin) 



Gemellus superior (origin) 



Gemellus inferior (origin) 



Semimembranosus (origin) 



Biceps and semitendinosus (origin) 



Quadratus femoris (origin) 



Obturator externus (origin) 



Adductor magnus (origin) 



^H^ -. 



Adductor magnus (origin) . 

 FIG. 369. MUSCLE-ATTACHMENTS TO THE RIGHT DORSUM ILII AND TUBER ISCHIADICUM. 



he muscle is inserted, for the most part, into the gluteal tuberosity ; but the most 

 nferior fibres of all are inserted into fascia lata, and are thereby connected with 

 he lateral intermuscular septum and the origin of the short head of the biceps. 



The glutseus maximus is the coarsest and heaviest muscle in the body. By its 

 weight it helps to form the fold of the nates. It is superficial in its whole extent, 

 ihe glutaeus medius is visible at its superior border, covered by the fascia lata ; at 

 ts lower border the hamstring muscles and sciatic nerve appear on their way to 

 he thigh. Three bursse are deep to it : one (not always present) over the sciatic 

 uberosity, a second over the lateral side of the greater trochanter, and a third 

 ver the vastus lateralis. The fibres of the glutseus maximus arising from the 

 occyx may form a separate muscle (agitator caudse). 



Nerve-Supply. Inferior gluteal nerve, from the sacral plexus (L. 5. S. 1. 2.). 



Actions. The glutaeus maximus is mainly an extensor of the thigh, and has a powerful 

 ction in straightening the lower limb, as in climbing or running. Its lower fibres also adduct 

 he thigh and rotate it laterally. 



M. Tensor Fasciae Latse. The tensor fasciae latae arises from the iliac crest 



