430 A MANUAL OF ANATOMY 



The intrapelvic and extrapelvic parts of the muscle form very 

 nearly a right angle with each other. It emerges from the pelvis 

 through the small sacro-sciatic foramen, and the deep surface of 

 its tendon is here broken up into from three to five columns, 

 separated from each other by grooves. The small sciatic notch 

 is covered by cartilage, which presents as many grooves as there 

 are columns on the deep surface of the tendon, these grooves being 

 separated by slight ridges. The grooves lodge the columns of the 

 tendon, and the ridges are received into the grooves between the 

 tendinous columns. A bursa intervenes between the tendon and 

 the cartilage covering the notch. 



Gemellus Inferior — Origin. — The upper part of the tuber ischii, 

 and the lower margin of the small sciatic notch. 



Insertion. — ^The lower border of the tendon of the obturator 

 internus. 



Nerve-supply. — Branch from the nerve to the quadratus femoris, 

 which enters the muscle on its deep or anterior surface near the 

 upper border, close to the origin. 



The gemelli muscles are merely extrapelvic origins of the obtu- 

 rator internus, of which they form accessory parts. As they take 

 insertion into the upper and lower borders of the obturator tendon 

 they are folded over it, so as to overlap and partially conceal the 

 tendon on its superficial aspect. They are auxiliary to the obturator 

 internus in action. 



Small Sacro-sciatic Foramen. — The structures which pass through this 

 foramen are as follows : (i) obturator internus ; (2) nerve to the obturator 

 internus ; (3) pudic nerve ; and (4) internal pudic artery with its venae comites. 



Quadratus Femoris — Origin. — The outer border of the tuber ischii. 



Insertion. — The linea quadrati of the femur, extending as low 

 as the small trochanter. 



Nerve-supply. — ^The nerve to the quadratus femoris from the 

 sacral plexus, which enters the muscle on its deep or anterior 

 surface near the upper border, close to the origin. 



Action. — External rotator of the thigh. 



The muscle conceals part of the obturator externus and the 

 small trochanter of the femur, from which latter it is separated by 

 a small bursa. When the gemellus inferior and quadratus femoris 

 are separated, part of the obturator externus comes into view. 

 Between the lower border of the muscle and the upper border 

 of the adductor magnus the transverse branch of the internal 

 circumflex artery appears, which here takes part in the crucial 

 anastomosis. When the lower border of the muscle is raised, the 

 small trochanter comes into view with the tendon of insertion of!' 

 the ilio-psoas. 



Arteries. — The chief arteries of the gluteal region are the gluteal, 

 sciatic, and internal pudic. 



Gluteal Artery. — This vessel arises from the posterior division;, 

 of the internal iliac^^iUwyf ""TlF'pci»g.^e parietal pelvic fascia, itf' 



