1 322 HUMAN ANATOMY. 



of its course it parallels the ilio-hypogastric, appearing at the edge of the psoas 

 magnus, crossing the quadratus lumborum behind the kidney and piercing the trans- 

 versalis to reach the intermuscular cleft between the transversalis and the internal 

 oblique (Fig. 1105). While in the last situation it inosculates with the ilio-hypo- 

 gastric and continues forward to enter the inguinal canal, from which it emerges 

 either through the external abdominal ring or through the external pillar of the 

 ring, infero-lateral to the spermatic cord. 



Some of the branches of the ilio-inguinal supply the integument of the upper inner portion 

 of the thigh. Others (nn. scrotales anteriores) are distributed to the pubic region and the base 

 of the penis and scrotum or, in the female (nn. labiales anteriores), the monsVeneris and labia 

 majora. Tiny motor filaments (rr. musculares) are given off in the course of the nerve to the 

 transversalis, the internal oblique and the external oblique. 



Variations. The ilio-inguinal may be small and terminate near the iliac crest by joining 

 the ilio-hypogastric, which then sends off an inguinal branch with the course and distribution of 

 the absent portion of the ilio-inguinal. The nerve may be absent entirely and replaced by either 

 branch, usually the genital, of the genito-crural. It may give off a lateral cutaneous or iliac 

 branch for the supply of the integument in the region of the anterior superior spine of the ilium. 

 The ilio-inguinal may partially replace the genital branch of the genito-crural or, in rare in- 

 stances, the external cutaneous. 



4. THE GENITO-CRURAL NERVE. 



The genito-crural nerve (n. genitofemoralis) is formed by two roots, one of which 

 arises from the loop between the first and second lumbar nerves and the other 

 directly from the second lumbar nerve, its fibres being derivatives of the first and 

 second lumbar. The nerve passes obliquely forward through the musculature of the 

 psoas magnus, near the inner border of whose anterior surface it emerges opposite 

 the body of the third lumbar vertebra, where division into the two terminal 

 branches, (a) the genital and (<) the crural, takes place (Fig. 1107). Occa- 

 sionally division occurs earlier in the course of the nerve, in the substance of the 

 psoas, and under these circumstances the two branches emerge separately from the 

 muscle. In addition to the terminal branches there are some (c) muscular twigs. 



a. The genital branch (n. spermaticus externus) obtains its fibres from the first lumbar 

 nerve. Passing downward on the inner margin of the psoas magnus, it crosses the external 

 iliac artery and bends forward toward the posterior wall of the inguinal canal. It then enters 

 the canal either by piercing the infundibuliform or the transversalis fascia and, lying internal to 

 and below the spermatic cord, traverses the canal and enters the scrotum (Fig. 1108). It sends 

 a filament to the external iliac artery and supplies the cremaster muscle, the skin of the scrotum 

 and the integument of the thigh immediately adjacent to the scrotum. In the female it is 

 smaller and accompanies the round ligament of the uterus to the labium majus, to whose in- 

 tegument it is distributed. It communicates with the ilio-inguinal nerve and with the spermatic- 

 plexus of the sympathetic. 



b. The crural branch (n. lumboinguinalis) consists of fibres from the second lumbar nerve. 

 It courses down on the anterior surface of the psoas magnus, lateral to the genital branch and 

 to the external iliac vessels, and enters the thigh by passing beneath Poupart's ligament. One 

 of its filaments traverses the saphenous opening, while the remainder of the nerve pierces the 

 fascia lata to the outer side of the opening (Fig. 1107). Its branches vary considerably in size 

 and length and are distributed to the cutaneous area of the upper anterior part of the thigh 

 between the regions supplied by the external cutaneous and ilio-inguinal nerves, sometimes 

 extending downward as far as the middle of the thigh. It furnishes a minute branch to the 

 femoral artery and inosculates with the middle cutaneous nerve. 



c. Muscular branches to the internal oblique and transversalis are frequently given off by 

 the genital branch. 



Variations. The genital and crural branches may arise as separate offshoots of the lumbar 

 plexus and either of them may be derived entirely from the first or the second lumbar nerve. 

 The genital branch sometimes contains fibres from the twelfth thoracic. Absence- of the genito- 

 crural or of either branch may occur, the fibres of the genital branch being contained in the ilio- 

 inguinal and thos- of the crural in the external cutaneous or the anterior crural. The genital 

 branch may replace or reinforce the ilio-inguinal nerve; the crural branch may act similarly 

 toward tin- external or the middle cutaneous nerve. A sjH-cimen found in the anatomical labo- 

 ratory of the I'niversity of Pennsylvania showed unusually extensive distribution of the crural 



