660 THE LUMBAR PLEXUS. 



ilio-inguinal nerves, and part of the genito-crural ; and to the latter belong 

 the remaining part of the genito-crural nerve, the external cutaneous, the 

 obturator, and the anterior crural nerves. 



ILIO-HYPOGASTRIC AND ILIO- INGUINAL NERVES. 



These nerves are the upper two branches from the lumbar plexus ; they 

 are both derived from the first lumbar nerve, and have a nearly similar 

 distribution. They become subcutaneous by passing between the broad 

 muscles of the abdomen, and through the outer one, and end in the integu- 

 ment of the groin and scrotum in the male, and the labia pudendi in the 

 female, as well as in the integument covering the gluteal muscles. The 

 extent of distribution of the one is inversely proportional to that of the 

 other. 



The ilio-hypogastric nerve, emerging from the upper part of the psoas 

 muscle at the outer border, 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 hypogastric branch. 



(a) The iliac branch pierces the attachment of both oblique muscles, immediately 

 above the iliac crest, and is lost in the integument over the gluteal muscles, behind 

 the distribution of the lateral cutaneous branch of the last dorsal nerve. 



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

 internal oblique muscles, 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 superficial inguinal opening, is distributed to 

 the skin of the abdomen above the pubes. 



The size of the iliac branch of this nerve varies inversely with that of the lateral 

 cutaneous branch of the twelfth dorsal. The hypogastric branch is not unfrequently 

 joined with the last dorsal nerve between the muscles, near the crest of the innominate 

 bone. 



The ilio-inguinal nerve, smaller than the preceding, supplies the integu- 

 ment of the groin. Descending obliquely outwards over the quadratus 

 lumborum, it crosses the fibres of the iliacus muscle, being placed lower 

 down than the ilio-hypogastric : it then perforates the transverse muscle 

 further forwards than the ilio-hypogastric ; communicating with that nerve 

 between the abdominal muscles. Then piercing the internal oblique muscle, 

 it descends in the inguinal canal, and emerging at the superficial inguinal 

 ring, is distributed to the skin upon the groin, as well as to that upon the 

 scrotum and penis ia the male, or the labium pudendi in the female, com- 

 municating with the inferior pudendal nerve. Tn its progress this nerve 

 furnishes branches to the internal oblique muscle. 



The ilio-inguinal nerve occasionally arises from the loop connecting the first and 

 second lumbar nerves. It is sometimes small, and ends near the iliac crest by joining 

 the ilio-hypogastric nerve ; in that case the last nerve gives off" an inguinal branch 

 having a similar course and distribution to the ilio-inguinal nerve, the place of which 

 it supplies. 



GENITO-CRURAL NERVE. 



The genito-crural nerve 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, 

 and afterwards on its fore part, towards Poupart's ligament, dividing at a 

 variable height into an internal or genital, and an external or crural branch. 



