402 ABDOMEN 



M. Iliacus. The iliacus muscle arises from the upper part 

 of the iliac fossa, the anterior sacro-iliac ligament, and the base 

 of the sacrum. It is inserted into the tendon of the psoas 

 major. Some of its fibres, however, have a separate insertion 

 into an impression below the lesser trochanter of the femur. 



It is supplied by a branch of the femoral nerve ; together 

 with the psoas major, it acts as a flexor and medial rotator 

 of the femur until the hip-joint is flexed, and then the two 

 muscles rotate the femur laterally. 



NERVES ON THE POSTERIOR WALL OF THE ABDOMEN. 



The nerves on the posterior wall of the abdomen are the 

 gangliated trunk of the sympathetic and the anterior rami 

 of the spinal nerves, with the branches which proceed from 

 them. These should now be dissected. 



Dissection. Clean the sympathetic trunks, one on each side. 

 They will be found along the anterior borders of the psoas major 

 muscles. On their lateral sides secure the branches which 

 connect their ganglia with the lumbar nerves, and on their 

 medial sides the branches they give to the aortic and hypogastric 

 plexuses. On the right side the inferior vena cava must be 

 displaced laterally to expose the right sympathetic trunk. 



Truncus Sympathicus. On each side, the sympathetic 

 trunk enters the abdomen behind the medial lumbo-costal 

 arch, and extends downwards upon the bodies of the lumbar 

 vertebrae along the anterior border of the psoas major muscle. 

 Superiorly^ it is continuous with the thoracic portion of the 

 trunk, whilst inferior ly, it passes behind the common iliac 

 artery and enters the pelvis minor. In the thorax, it is placed 

 upon the heads of the ribs ; in the abdomen it lies nearer 

 the median plane, being carried forwards by the psoas major 

 muscle. On the right side it is covered by the inferior vena 

 cava, and on both sides the lumbar vessels pass behind it. 

 As a general rule, a small oval ganglion is formed upon it 

 opposite the body of each lumbar vertebra. Rami com- 

 municantes and peripheral branches of distribution proceed 

 from the gangliated trunk. 



The rami communicantes connect the ganglia with the 

 anterior rami of the lumbar spinal nerves. One or more will 

 be found accompanying each lumbar artery. Trace them 

 backwards by cutting through the fibrous arches which bridge 



