168 



DISSECTION OF THE THIGH. 



parts 

 around ; 



use. 



Obturator 

 externus 



origin ; 



insertion. 



The adduc- 

 tors cover 

 it; 



and it 



touches 



hip-joint. 



Use. 



Detach 

 obturator. 



Obturator 

 artery 



divides into 

 two: 



inner, 



and outer 

 branch. 



Branches of 

 the nerve. 



fibres are fixed into a special triangular surface of bone in front of 

 and below the trochanter (fig. 61). 



These muscles occupy the interval beneath Poupart's ligament 

 between the ilio-pectineal eminence and the anterior superior iliac 

 spinous process ; and below the pelvis the mass covers the capsule 

 of the hip-joint, a large bursa intervening. On the front of the 

 psoas is the common femoral artery, and between the two muscles 

 lies the anterior crural nerve. The pectineus and the internal 

 circumflex vessels are contiguous to the inner border, and the 

 sartorius and vastus internus touch the outer edge. 



Action. These muscles act as flexors of the hip-joint ; and the 

 use of the psoas on the spinal column will be given with the 

 description of the muscle in the abdomen. 



The OBTURATOR EXTERNUS (fig. 62, F) is triangular in form, 

 with the base at the pelvis and the apex at the femur. The fibres 

 of the muscle take origin from the outer surface of the obturator 

 membrane for the inner half, and from the bony circumference of the 

 thyroid foramen for a corresponding extent, the bony attachment 

 being an inch wide opposite the body of the pubis, and reaching 

 inwards to the adductor brevis and magnus (fig. 47, p. 113). The 

 fibres are directed backwards and outwards to be inserted by a 

 tendon into the pit at the root of the great trochanter. 



This muscle is concealed by the pectineus, and adductor brevis 

 and magnus. It covers the obturator membrane and vessels, and 

 is pierced by the deep part of the obturator nerve. As it winds 

 back it is in contact with the lower surface of the hip-joint. The 

 insertion of the muscle has been seen in the dissection of the 

 buttock (p. 123). 



Action. The muscle is an external rotator of the thigh, and to 

 a slight extent an adductor and flexor of the hip- joint. 



Dissection. By detaching the obturator muscle from the pelvis, 

 the branches of the artery of the same name will be seen beneath 

 its fibres. The deep part of the nerve may be followed back to 

 the foramen at the same time. A better view will be obtained if 

 this dissection is deferred till after the limb is removed. 



The OBTURATOR ARTERY is a branch of the internal iliac within 

 the pelvis, and enters the thigh through the top of the thyroid 

 foramen. In the aperture the artery divides into two branches, 

 which form a circle on the obturator membrane beneath the muscle : 



The internal branch runs along the inner half of the membrane, 

 and furnishes offsets to the obturator externus and the upper ends 

 of the adductor muscles. 



The external branch descends close to the outer edge of the 

 foramen, and after giving a branch inwards to join the lower end 

 of the preceding, is continued to the ischial tuberosity and the 

 muscles arising therefrom. Offsets pass to both obturator muscles ; 

 and an articular twig is given to the hip-joint. 



The nerves to the obturator externus come from the deep por- 

 tion of the obturator, and enter the posterior surface of the muscle. 



