BRANCHES OF LUMBAR PLEXUS. 315 



thigh. The extent of distribution of the one is inversely proportional to that of the 

 other. 



The ilio-hypogastric nerve, the highest and largest of the branches proceed- 

 ing from the first lumbar nerve, usually receives fibres also from the last dorsal 

 nerve through the dorse-lumbar cord. Issuing from the upper part of the psoas 

 muscle at the outer border, it runs obliquely over the quadratus lumborum to the 

 iliac crest, and there perforating the transverse muscle of the abdomen, gets between 

 that muscle and the internal oblique, and divides into an iliac and a hypogastric 

 branch. 



(a) The iliac branch (ramus cutancus lateralis) pierces the internal oblique 

 muscle, and then emerges through the external oblique close to the iliac crest about 

 the junction of its middle and anterior thirds, to be distributed to the integument 

 over the gluteus medius and tensor vaginae femoris muscles. 



(b) The hypogastric or abdominal branch passes on between the transversalis and 

 internal oblique muscles, to both of which it supplies twigs, and is connected with 

 the ilio-inguinal nerve near the iliac crest. It then perforates the internal oblique 

 muscle, and, piercing the aponeurosis of the external oblique a little above the 

 external abdominal ring, is distributed to the skin of the abdomen above the pubis 

 (r. cutaneus anterior). 



Varieties. The ilio-hypogastric nerve is occasionally derived from the last dorsal, and it 

 may even receive a root from the eleventh dorsal nerve (fig-. 205, A). The iliac branch varies 

 in size inversely with the lateral cutaneous of the twelfth dorsal, and it is sometimes altogether 

 wanting-. The hypogastric branch is not unfrequently joined with the last dorsal nerve 

 between the muscles. In some cases this branch supplies the pyramidalis muscle. 



The ilio-inguinal nerve, smaller than the preceding, is also derived from the 

 first lumbar nerve, and sometimes receives an accession from the dorso-lurnbar cord. 

 Appearing from beneath the outer border of the psoas muscle below the ilio-hypo- 

 gastric nerve, it is directed obliquely downwards and outwards over the quadratus 

 lumborum and iliacus to the fore part of the iliac crest, where it perforates the 

 transversalis, and communicates with the ilio-hypogastric nerve between the 

 muscles. Then piercing the internal oblique muscle, it descends in the inguinal 

 canal, and emerging at the external abdominal ring on the outer side of the 

 spermatic cord, divides into branches which are distributed to the skin of the pubic 

 region and root of the penis and scrotum in the male, or labium pudendi in the 

 female (nn. scrotales s. labiales anteriores), and of the adjacent upper and inner 

 part of the thigh. In its progress this nerve may furnish branches to the internal 

 oblique and transversalis muscles. 



Varieties. The ilio-hypogastric and ilio-inguinal nerves often arise by a common trunk, 

 which divides after perforating the transversalis muscle. The ilio-inguinal nerve is occasion- 

 ally derived from the last dorsal nerve (fig. 205, A). On the other hand, it may spring from 

 the loop between the first and second lumbar nerves, or even entirely from the latter nerve. 

 It is sometimes small, and ends near the iliac crest by joining the ilio-hypogastric nerve, 

 which in that case gives off an inguinal branch having a similar course and distribution to the 

 ilio-inguinal nerve. The ilio-inguinal nerve may be absent, its place being taken by the 

 genital, rarely by the crural, branch of the genito-crural. In some cases the nerve has an 

 iliac or lateral branch, which is distributed to the skin in the neighbourhood of the anterior 

 superior iliac spine. The ilio-inguinal nerve may also replace to a greater or less extent the 

 genital branch of the genito-crural. or (very rarely) the external cutaneous -nerve (M. Griffin). 



Genito-crural nerve. The genito-crural nerve (n. geniiofemoralis) belongs 

 partly to the external genital organs and partly to the thigh. It is derived chiefly 

 from the second lumbar nerve, but receives also a few fibres from the connecting 

 cord between that and the first nerve. The nerve descends obliquely through the 

 psoas muscle, from which it emerges near the inner border, about on a level with 



