1000 THIE NERVOUS SYSTEM 



The ilio-inguinal nerve arises principally from the first lumbar nerve, but it 

 frequently contains fibres of the last thoracic nerve. It emerges from the lateral 

 border of the psoas, at a lower level than the iho-hypogastric nerve, and passes 

 across the quadratus lumborum (figs. 765, 766). As a rule, it is below the level 

 of the inferior end of the kidney, but it passes dorsal to the ascending or the 

 descending colon according to the side considered, and crosses the posterior part 

 of the inner lip of the iliac crest; it then runs forward on the upper part of the 

 iliacus, pierces the transverus abdominis near the anterior part of the crest, and 

 communicates with the anterior cutaneous (hypogastric) branch of the ilio- 

 hj^pogastric nerve. A short distance below the anterior superior spine it passes 

 through the internal oblique muscle, and then descends in the inguinal canal to 

 the subcutaneous inguinal (external abdominal) ring, through which it emerges 

 into the thigh on the lateral side of the spermatic cord (fig. 763). It is distributed 

 to the skin of the upper and medial part of the thigh, in the male to the root of the 

 penis and to the skin of the root of the scrotum through the anterior scrotal 

 nerves (fig. 768), and in the female to the mons veneris and labium majus through 

 the anterior labial nerves. 



Not uncommonly the ilio-inguinal nerve is blended with the ilio-hypogastric nerve and 

 separates from the latter between the transversus abdominis and the internal obUque muscles. 

 It may be replaced by branches of the genito-femoral (genito-crural) nerve, or it may replace 

 that nerve or the lateral cutaneous nerve. 



The genito-femoral (genito-crural) nerve is connected with the first and 

 second lumbar nerves, but the majority of its fibres are derived from the second 

 nerve. It passes obliquely forward and downward through the psoas and emerges 

 from the anterior surface of that muscle, close to its medial border, at the level 

 of the lower border of the third lumbar vertebra. After emerging from the sub- 

 stance of the psoas it runs downward on the anterior surface of the muscle 

 (fig. 765), to the lateral side of the aorta and the common iliac artery, passes 

 behind the ureter and divides into two branches, an external spermatic or genital, 

 and a lumbo-inguinal or crural (fig. 766). Occasionally it divides in the substance 

 of the psoas, and then the two branches issue separately through the anterior 

 surface of the muscle. 



The external spermatic (genital) branch runs downward on the psoas muscle, external to 

 the external iliac artery; it gives a branch to the psoas, and at Poupart's ligament it turns 

 around the inferior epigastric artery and enters the inguinal canal, accompanying the spermatic 

 cord in the male or the round hgament in the female. It suppHes the cremaster muscle, and 

 gives twigs to the integument of the scrotum (fig. 766) or the labium majus. 



The lumbo-inguinal (crural) branch passes downward along the external ihac artery and 

 beneath Poupart's hgament into the thigh, which it enters to the lateral side of the femoral 

 artery. A short distance below Poupart's ligament it pierces the fascia lata or passes through 

 the fossa ovahs (saphenous opening) and supplies the skin in the middle of the upper part of the 

 thigh. A short distance below Poupart's hgament it sometimes sends branches to the anterior 

 branch of the lateral cutaneous nerve, and about the middle of the thigh it often joins with the 

 cutaneous branches of the femoral (anterior crural) nerve. 



The lateral cutaneous nerve receives fibres from the dorsal branches of the 

 anterior primary divisions of the second and third lumbar nerves, and frequently 

 some fibres from the first lumbar (fig. 769). It emerges from the lateral border 

 of the psoas and passes obliquely across the iliacus dorsal to the iliac fascia, and 

 dorsal to the ciccum on the right side and the sigmoid colon on the left side, to a 

 point imnKHliately below the anterior superior spine of the ilium, where it passes 

 Ijelow Poupart's ligament into the lateral angle of the femoral trigone (Scarpa's 

 triangle). Leaving the trigone at once it passes through, behind, or in front of 

 the sartorius and divides into two branches, anterior and posterior, which enter 

 the deep fascia (fig. 766). 



The posterior branch of the lateral cutaneous nerve breaks up into several secondary 

 branches which become subcutaneous, and they supply the integument of the lateral part of the 

 thigli, from the great trochanter to the level of the middle of tlif^ fenmr. The anterior branch 

 runs downward in a canal in the deep fascia, for three or four inches, before it becomes sub- 

 cutaneous. It usually divides into two branches, a lateral and a medial. The lateral branch 

 8upi)lics the skin of the lower half of the lateral side of the thigli, and the vicdial branch is dis- 

 tributed to the skin of the lateral side of tl)e front of the tliigh as far as the knee (fig. 766). 

 Its lower filaments frequently unite with the cutaneous branches of the femoral (anterior 



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