580 DISSECTION OF THE THIGH. 



The PSOAS and ILIACUS (fig. 198) arise separately in the abdomen (p. 

 493), but are united in the thigh the conjoined portion of the muscles 

 coming beneath Poupart's ligament. The psoas, P, is inserted by tendon 

 into the small trochanter of the femur : and the fleshy iliacus, o, joins 

 partly the tendon of the psoas, tut the rest of its fibres are fixed into a 

 special triangular surface of bone in front of and below that trochanter. 



Beneath the ligament the muscles occupy the interval between the ilio- 

 pectineal eminence and the anterior superior iliac spinous process the 

 iliacus resting on a small bursa ; and below the pelvis the mass covers the 

 capsule of the hip joint, and a larger intervening bursa. On the front of 

 the psoas is the femoral artery, and between the two muscles lies the an- 

 terior 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 their use is 

 given with the description of the part in the abdomen (p. 493). 



The OBTURATOR EXTERNUS (fig. 198, 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 an- 

 terior half ; and from the anterior half or more of the bony circumference 

 of the thyroid foramen the attachment being an inch wide opposite the 

 symphysis pubis. The fibres are directed obliquely backwards to be in- 

 serted 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 

 part of the obturator nerve. As it winds back it is in contact with the 

 inner and lower parts of the hip joint. The insertion of the muscle will 

 be seen in the dissection of the Buttock. 



Action. The muscle is an external rotator of the thigh : and its action 

 will be given in full with the other muscles of the same group in the 

 Buttock. 



Dissection By detaching a small part of the obturator muscle from 

 the pelvis, the branches of the artery and nerve of the same name will 

 be seen amongst its fibres. A better view will be obtained if the dissec- 

 tion of the vessel and nerve is deferred till after the limb is detached. 



The obturator artery is a branch of the internal iliac (p. 515), and 

 enters the thigh through the upper part of the thyroid foramen. In the 

 aperture the artery divides into two pieces, which form a circle beneath 

 the muscle around the obturator membrane : 



The upper branch extends along the inner half of the membrane ; and 

 the lower, perforating the membrane below the level of the other, turns 

 downwards and forms a circle by uniting with the upper branch. An 

 articular twig to the hip-joint is supplied from the lower branch. 



Muscular offsets of the artery are furnished to the obturator muscles, 

 and some small twigs reach the upper part of the adductors. 



Branches of nerve to the external obturator muscle come from the deep 

 portion of the obturator trunk, and perforate the membrane with the lower 

 branch of the artery. 



