55 ABDOMEN 



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

 into an impression below the lesser trochanter of the femur. 



NERVES ON THE POSTERIOR WALL OF THE ABDOMEN. 



The nerves on the posterior wall of the abdomen are the 

 gangliated cord of the sympathetic and the anterior primary 

 divisions of the spinal nerves, with the branches which proceed 

 from them. These should now be dissected. 



Gangliated Cord of the Sympathetic. On each side 

 this enters the abdomen behind the arcus lumbo-costalis 

 medialis, and extends downwards upon the bodies of the 

 lumbar vertebrae along the anterior border of the psoas 

 magnus muscle. Above it is continuous with the thoracic 

 portion of the cord, whilst below it passes behind the common 

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

 upon the heads of the ribs ; in the abdomen, however, 

 it lies nearer the median plane, being carried forwards by the 

 psoas magnus muscle. On the right side, it is in great 

 part covered by the inferior vena cava, and on both sides the 

 lumbar vessels pass laterally behind it. As a general rule, a 

 small oval ganglion is formed upon the body of each lumbar 

 vertebra. Rami communicantes and peripheral branches of 

 distribution proceed from the ganglionic cord. 



The rami communicantes connect the ganglia with the 

 anterior primary divisions 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 over these vessels and scraping away the fibres 

 of the psoas muscle. .They join the lumbar nerves close to 

 the intervertebral foramina. 



The rami communicantes consist of two sets, viz. white and grey. 

 The white rami communicantes are composed of medullated fibres which 

 pass from the spinal nerves to the gangliated cord. In the lumbar region 

 there are only two or at most three of these, and they proceed from the 

 upper two or three lumbar nerves. The grey rami communicantes are 

 much more numerous, and are formed of fibres which stream out in an 

 irregular manner from the sympathetic cord to all the anterior primary 

 divisions of the lumbar nerves. 



The peripheral branches of distribution consist of a large 

 number of small filaments which arise irregularly from the 

 lumbar gangliated cord and pass medially to the aortic plexus. 



