INTERNAL CIRCUMFLEX ARTERY. 123 



found divided into four or five pieces as it turns over the ischium 

 tig. 50, H) ; at this spot the bone is covered with cartilage, which 

 brms ridges corresponding to the intervals between the tendinous 

 lips, and the surfaces are lubricated by a sy no vial sac. There is 

 sometimes another bursa between the tendon and the hip-joint. 



Action. The action of this muscle is in all respects the same as use like 

 that of the pyriformis (p. 1 1 8), although, as it acts at a greater py riformis - 

 iiHrhanical advantage, it is a much more powerful external rotator. 



The QUADRATUS FEMORIS (fig. 48, G) is situate between the Quadratus 

 nferior gemellus and the adductor niagnus. Internally it arises fei 

 rom the outer border of the ischial tuberosity for two inches, by the ongm ; 

 ide of the semimembranosus and adductor magnus (fig. 47, p. 113); 



ernally it is inserted into an eminence on the posterior inter- insertion ; 

 rochanteric ridge of the femur (tubercle of the quadratus), and 

 ilong a line on the upper end of that bone for about one inch and a 

 lalf, above the attachment of the great adductor (fig. 61, p. 158). 



By one surface it is in contact with the sciatic vessels and nerves, parts over 

 ind the glutens maxinius. By the other it rests on the obturator and beneath 

 xternus, the internal circumflex vessels, and its small nerve and ' 

 vessels. Between its lower border and the adductor magnus the and at lower 

 iransverse branch of the internal circumflex artery issues. Between 

 t and the small trochanter is a bursa, which is also common to the 

 upper part of the adductor magnus. 



Action. The quadratus differs from the foregoing muscles of the use- 

 same group in l>eing able to rotate the femur outwards when the 

 lip-joint is bent, as well as in the extended position ; and it will 

 assist slightly in adducting the limb. 



Dissection (fig. 50). The quadratus and the gemelli muscles Divide 

 may now be cut across, in order that their small nerve and artery, quadratus 

 he ending of the internal circumflex artery, and the obturator a " 

 .xternus may be dissected out. 



The INTERNAL CIRCUMFLEX ARTERY (fig. 50) from the profunda f?tj 

 'emoris artery (p. 166) divides finally into two pieces. One 

 a swirling) runs beneath the quadratus (in this position of the 

 >ody) to the pit of the trochanter, where it anastomoses with the 

 gluteal and sciatic arteries, and supplies the bone. The other ends in two 

 transverse) passes between the quadratus and adductor niagnus branches - 

 o the hamstring muscles, and communicates with the perforating 

 rteries. 



The OBTURATOR EXTERNUS (fig. 50, L) will be dissected at its Obturator 



>rigin in the front of the tbigh. The part of the muscle now laid e> 



bare winds below the hip-joint, and ascends to be inserted into the is inserted 



L .LI f ^i 1 into pit of 



pit at the root of the trochanter. trociianter ; 



On the back of the pelvis the obturator externus is covered by the relations ; 

 quadratus, except near the femur where it is exposed between that 

 muscle and the inferior gemellus. Its deep surface is in contact 

 with the capsule of the hip-joint and the neck of the femur. 



Action. Like the quadratus femoris, it rotates the femur out- use. 

 wards in all positions of the limb : it is also to a slight extent an 

 adductor and flexor of the hip-joint. 



