496 



DISSECTION OF THE ABDOMEN. 



the common trunk ; and from this, before it enters the sacral plexus, arises 

 the superior gluteal nerve (*), 



The LUMBAR PLEXUS (tig. 172) is formed by the intercommunication 

 of the first four lumbar nerves. Contained in the substance of the psoas 

 near the posterior surface, it consists of communicating loops between the 

 several nerves, and increases in size from above downwards, like the in- 

 dividual nerves. Superiorly it is sometimes united by a small branch with 

 the last dorsal nerve ; and inferiorly it joins the sacral plexus through the 

 large lumbo-sacral cord. 



Fig. 172. 



CD 



o 

 O 



I "*,. 



1} - 



a. External iliac artery, cut across. 

 6. Thoracic duct. 



c. Azygos vein. 



Nerves : The figures 1 to 5 mark the 

 trunks of the five lumbar nerves. 



d. Splanchnic nerves. 

 . Last dorsal. 



/. Ilio-hypogastric. 

 g. Ilio-inguinal. 

 h. Genito-crural. 



f. External cutaneous. 



k. Anterior crural. 



I. Accessory to obturator. 

 n. Obturator. 

 o. Gangliated cord of the sympathetic. 



DISSECTION OF THE LUMBAR PLEXUS AND ITS BRANCHES. (Illustrations of Dissections.) 



The branches of the plexus are six in number, and supply the lower 

 part of the abdominal wall and muscular covering of the spermatic cord, 

 the fore part of the thigh, and the inner side of the leg. 



The first two branches (ilio-hypogastric and ilio-inguinal) end as cutane- 

 ous nerves of the buttock, lower part of the abdomen, and the scrotum. 



a. The ilio-hypogastric branch (fig. 172, f) is derived from the first 

 nerve, and appears at the outer border of the psoas muscle, near the upper 

 part. It is directed over the quadratus lumborum to the iliac crest, and 

 enters the wall of the abdomen by penetrating the transversalis abdominis. 



