938 THE NERVOUS SYSTEM 



psoas it runs downwards on the anterior .surface of the muscle (fig. 688), to the outer 

 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. 689). 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 downwards 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 ligament in the female. 

 It supplies the cremaster'muscle, and gives twigs to the integument of the scrotum 

 (fig. 689) or the labium majus. 



The lumbo-inguinal (crural) branch passes downwards along the external iliac 

 artery and beneath Poupart's ligament into the thigh, which it enters to the outer side 

 of the femoral artery. A short distance below Poupart's ligament it pierces the fascia 

 lata or passes through the fossa ovalis (saphenous opening) and supplies the skin in 

 the middle of the upper part of the thigh. A short distance below Poupart's liga- 

 ment it sometimes sends branches of communication to the anterior branch of the 

 lateral cutaneous nerve, and about the middle of the thigh it often communicates 

 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. 693). It emerges from the outer border of the 

 psoas and passes obliquely across the iliacus behind the iliac fascia, and behind the 

 caecum on the right side and the sigmoid colon on the left side, to a point immediately 

 below the anterior superior spine of the ilium, where it passes below Poupart's liga- 

 ment into the outer 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. 689). 



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

 secondary branches which become subcutaneous, and they supply the integument of 

 the outer part of the thigh, from the great trochanter to the level of the middle of 

 the femur. The anterior branch runs downwards in a canal in the deep fascia, for 

 three or four inches, before it becomes subcutaneous. It usually divides into two 

 branches, an external and an internal. The external branch supplies the skin of the 

 lower half of the outer side of the thigh, and the internal branch is distributed to the 

 skin of the outer side of the front of the thigh as far as the knee (fig. 689). Its lower 

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

 crural), and with the patellar branch of the saphenous nerve in front of the patella, 

 forming with them the patellar plexus. 



The Femoral (Anterior Crural) Nerve is the largest branch of the lumbar plexus. 

 It is formed principally by fibres of the dorsal branches of the anterior primary 

 divisions of the second, third, and fourth lumbar nerves, but it sometimes receives 

 fibres from the first nerve also (figs. 688 and 693) . It emerges from the outer border 

 of the psoas a short distance above Poupart's ligament, and descends in the groove 

 between the psoas and the iliacus, behind Poupart's ligament, into the femoral trigone 

 (Scarpa's triangle), where it lies to the outer side of the femoral artery (fig. 690), 

 from which it is separated by some of the fibres of the psoas. In this situation it is 

 flattened out and it divides into two series of terminal branches, the superficial and 

 the deep. 



Branches. The branches are collateral and terminal. 



The collateral branches are twigs of supply to the iliacus, and a branch to the 

 femoral artery ; they are given off before the nerve enters the femoral trigone. 



The terminal branches form two groups, the superficial and the deep. 



The superficial terminal branches are two muscular branches, the nerve to 

 the pectineus, and the nerve to the sartorius, and two anterior cutaneous branches. 



The nerve to the pectineus passes inwards and downwards behind the femoral 

 sheath and in front of the psoas to the anterior surface of the pectineus, in which 

 it terminates. 



The nerve to the sartorius accompanies the middle cutaneous nerve; it leaves 

 the latter nerve above the sartorius and ends in the upper part of the muscle. 



The anterior (middle and internal) cutaneous nerves are best described sepa- 

 rately. The middle cutaneous nerve soon divides into two branches, inner and outer. 



