782 



THE NERVOUS SYSTEM. 



the whole of the posterior division of the fourth lumbar nerve to form the anterior 

 crural. The accessory obturator, when it exists, is formed by the union of two 

 small branches given off from the third and fourth nerves. 



jlin-hypogastric 



thL 



FIG. 416. Plan of the lumbar plexus. 



From this arrangement it follows that the ilio-hypogastric and ilio-inguinal 

 are derived entirely from the first lumbar nerve ; the genito-crural from the first 

 and second nerves ; the external cutaneous from the second and third ; the ante- 

 rior crural and obturator by fibres derived from the second, third, and fourth ; 

 and the accessory obturator, when it exists, from the third and fourth. 



The branches of the lumbar plexus are the 



Ilio-hypogastric. 

 Ilio-inguinal. 

 Genito-crural. 

 External cutaneous. 



Anterior crural. 

 Obturator. 

 Accessory obturator. 



The Ilio-hypogastric Nerve arises from the first lumbar nerve. It emerges from 

 the outer border of the Psoas 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 at its posterior part near the crest of the ilium, and divides 

 between it and the Internal oblique into two branches, iliac and hypogastric. 



The iliac branch pierces the Internal and External oblique muscles immediately 

 above the crest of the ilium, and is distributed to the integument of the gluteal 

 region, behind the lateral cutaneous branch of the last dorsal nerve (Fig. 422). 

 The size of this nerve bears an inverse proportion to that of the cutaneous branch 

 of the last dorsal nerve. 



The hypogastric branch (Fig. 418} continues onward between the Internal 

 oblique and Transversalis muscles. It then pierces the Internal oblique, and 

 becomes cutaneous by perforating the aponeurosis of the External oblique, about 



