372 



DISSECTION OF THE ABDOMEN. 



Four lumbar 

 nerves enter 

 plexus 



and supply 

 muscles : 



fifth to the 



sacral 



plexus. 



Plexus how 

 formed ; 



situation ; 



connections 

 with nerves. 



Six 



branches, 

 viz. : 



Two 



cutaneous 



branches. 



Ilio-hypo- 

 gastric : 



course in 

 abdomen. 



Ilio-inguinal 

 arises with 

 preceding, 



and accom- 

 panies it. 



Genito- 

 crural 



pierces 



and divides 

 into 



genital and 



On the right side the psoas is to be left untouched, in order that 

 the place of emergence from it of the different offsets of the plexus 

 may be noticed. 



LUMBAR SPINAL NERVES. The anterior primary branches of the 

 lumbar nerves, five in number, increase in size from above down, 

 and are joined by filaments of the sympathetic near the interveite- 

 bral foramina. With the exception of the last, they enter the 

 lumbar plexus, having previously given off branches for the supply 

 of the quadratus lumborum and psoas muscles. 



The fifth nerve receives a communicating branch from the 

 fourth, and is to be followed into the pelvis to its junction with 

 the sacral plexus. After the two are united, the name Inmbo-sacral 

 cord is applied to the common trunk. 



The LUMBAR PLEXUS (fig. 140) is formed by the intercommunica- 

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

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

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

 individual 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. 



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

 part of the abdominal wall and the muscular covering of the sper- 

 matic cord, the fore and inner parts of the thigh, and the inner side 

 of the leg. 



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

 cutaneous nerves of the hip, the lower part of the abdomen, the 

 scrotum, and the thigh. 



1. The ilio-hypogastric branch (fig. 140, /) is derived from the first 

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

 upper end. It is directed over the quadratus lumborum to the iliac 

 crest, and enters the wall of the abdomen by piercing the transversalis 

 muscle. Its termination in the integuments of the buttock and 

 abdomen, by means of an iliac and a hypogastric branch has been 

 already mentioned (pp. 110, 263 and 275). 



2. The ilio-inguinal branch (g] arises with the preceding from the 

 first nerve, and issues from the psoas nearly at the same spot. Of 

 smaller size than the ilio-hypogastric, this branch courses outwards 

 over the quadratus and iliacus muscles towards the front of the iliac 

 crest, where it pierces the transversalis. The farther course of the 

 nerve in the abdominal wall, and its distribution to the scrotum and 

 the thigh, are before noticed (pp. 264 and 275). 



3. The genito-crural nerve (h) is distributed to the cremaster muscle 

 and the limb. It arises from the second lumbar nerve, and from the 

 connecting loop between the first two ; issuing from the front of the 

 psoas, it descends on the surface of the muscle, and divides into 

 genital and crural branches. Sometimes the nerve is divided in the 

 psoas, and the branches perforate the muscle separately. 



The genital branch descends on the external iliac artery, and 

 furnishes offsets around it : it passes from the abdomen with the 



