212 Study of the Abdominal and Border-Nerves in Man 



ment to the ventral portion of the iliac crest the internal oblique muscle 

 is often divided into two layers, and between the layers another channel 

 is offered for the passage of the inguinal and hypogastric branches. 

 But while the regions in which the hypogastric and inguinal nerves pass 

 from the channel between the transversalis fascia and the transversalis 

 muscle to that between the latter and the internal oblique muscles, and 

 from this to the channel between the two layers of the internal oblique 

 and thence to that between the internal oblique and the tendon of the 

 external oblique, vary in different individuals, the general course of 

 these nerves is fairly constant. On the other hand, there are no definite 

 paths of guidance for the genito-crural nerves. They take an irregular 

 course from the anterior region of the lumbo-sacral plexus through the 

 psoas muscle and behind the transversalis fascia to the region of Pou- 

 part's ligament. Here the genital nerve pierces the transversalis and 

 internal oblique muscles or their tendon enters the channel between 

 the latter and the tendon of the external oblique, fuses here with the 

 inguinal nerve, and is distributed in common with the branches of the 

 latter nerve. The crural nerve, on the other hand, passes beloAv Pou- 

 part's ligament and supplies the skin of the leg near the region of its 

 junction with the abdomen. Either or both nerves may give off 

 branches to the external iliac and femoral arteries. 



In origin, the genito-crural nerves vary no more than the otlier border- 

 nerves. Thus, from Table Y it will be seen that the genito-crural nerves 

 arise from the 21st nerve in 56 instances, 19;^ (in a certain number of 

 these some fibres are derived from the 20th also); from the 21st and 

 22nd in 125 instances, 79;^; and in but 6 instances, 2^, from the (21st), 

 22nd and 23rd. 



There is considerable variation in the number of nerves designated 

 " genito-crural .'' Most commonly (in 154 instances out of 250 of which 

 good records are preserved, 61.6^), the genital and crural branches are 

 bound in a common trunk, which, at a variable distance above Poupart's 

 ligament, divides into genital and crural branches. Not infrequently, 

 in addition to such a trunk, there is an extra genital branch (16 in- 

 stances, 6.4^), or an extra crural branch (25 instances, 10^). Occasion- 

 ally no crural branch is found (3 instances, 1.2^); more often the genital 

 branch is wanting (17 instances, 6.8;^). I have seen no instances in 

 which both branches were wanting. 



The regions of exit of the genital nerve into the path taken by the 

 inguinal nerve and of the crural nerve into the superficial fascia of the 

 thigh, vary greatly. The genital nerve may pass into the path of the 

 inguinal not far from the anterior superior spine of the ilium (lateral 



