1048 



THE NER VE SYSTEM 



The mode in which the plexus is arranged varies in different subjects. 1 It 

 differs from the brachial plexus in not forming an intricate interlacement, but the 

 several nerves of distribution arise from one or more of the spinal nerves in the 

 following manner: The first lumbar nerve receives a branch from the last tho- 

 racic, gives off a larger, 

 upper branch, which sub- 

 divides into the iliohypo- 

 gastric and ilio inguinal 

 nerves; and a smaller 

 lower branch which unites 

 with a branch of the 

 second lumbar, to form 

 the genitofe moral nerve. 

 The remainder of the 

 second nerve and the 

 third and fourth lumbar 

 nerves divide into anterior 

 and posterior divisions. 

 The anterior division of 

 the second unites with the 

 anterior division of the 

 third nerve and a part of 

 the anterior division of 



jBiwnMiwnfc* 

 OBTURATOR\\ X 



FIG. 768. Diagram of the lumbar plexus. 



ILIOHYPOGASTRIC 

 ILIO-INGUINAL 



GENITOFEMORAL 



EXTERNAL 

 CUTANEOUS 



TO PSOAS AND 



ILIACUS 



FEMORAL (ANTERIOR 

 CRURAL) 



the fourth nerve to form 

 the obturator nerve. The 

 remainder of the anterior 

 division of the fourth nerve passes down to communicate with the fifth lumbar 

 nerve. The posterior divisions of the second and third nerves divide into two 

 branches, a smaller branch from each uniting to form the external or lateral 

 cutaneous nerve, and a larger branch from each, joining with the posterior division 

 of the fourth lumbar nerve to form the femoral or anterior crural nerve. The 

 accessory obturator, when it exists, is formed by the union of two small branches 

 given off from the third and fourth nerves. 



The branches of the lumbar plexus may therefore be arranged as follows : 



Iliohypogastric 1 , L. 



Ilioinguinal 1,L. 



Genitofemoral . 1 , 2. L. 



Dorsal Divisions. 



External (or lateral) cutaneous 2, 3, L. 



Femoral (or anterior crural) 2, 3, 4, L. 



Ventral Divisions. 



Obturator 2, 3, 4, L. 



Accessory obturator 3, 4, L. 



The Iliohypogastric Nerve (n. iliohypogastricus) (Figs. 768 and 769) arises from 

 the first lumbar nerve. It emerges from the lateralborder of the Psoas magnus 

 muscle at its upper part, and crosses obliquely in front of the Quadratus lumborum 

 to the crest of the ilium. It then perforates the Transversalis muscle posteriorly 

 near the crest of the ilium. It gives off muscular branches (rami musculares) to 

 the abdominal wall, and divides between the Transversalis and the Internal oblique 

 into two cutaneous branches, iliac and hypogastric. 



1 For statistical studies of the variations encountered in different individuals, see the article by Bardeen, in 

 the American Journal of Anatomy, vol. vi. 



