THE LUMBAR PLEXUS. 199 



THE LUMBAR PLEXUS. 



The dissection of the lumbar plexus presupposes the removal of the 

 peritoneum and cellular tissue in the lumbar region ; the nerves 

 composing it- are mostly small in size, and though liable to be divided 

 in the dissections already made, their origin and a portion of their 



urse may always be demonstrated. 



The LUMBAR PLEXUS is formed by the communications 

 of the anterior branches of the five lumbar nerves ; the 



rterior branches being distributed to the muscles of the 

 k. The principal trunks are the following, viz : 

 Musculo-cutaneous, Crural, 



External Cutaneous, Obturator, 



Genito-crural, Lumbo-sacral. 



The mnsculo-cutaneous nerve, coming from the first lumbar nerve, 

 crosses the quadratus lumborum muscle obliquely, to reach the mid- 

 dle of the crest of the ilium, where it pierces the transversalis muscle, 

 and divides into two branches, the abdominal and the scrotal ; the 

 hduminal supplying the muscles and integument of the abdomen ; 

 scrotal, joining the spermatic cord in the male, and the round 

 gament in the female, at the external inguinal ring, is distributed 



the integument of the scrotum, or, in the female, to- the labia 

 ajora. 



The external cutaneous nerve, coming from the second lumbar nerve, 

 crosses the iliacus interims muscle obliquely, to reach the anterior 

 superior spinous process of the ilium, where it passes underneath 

 Toupart's ligament, and is distributed to the integument of the gluteal 

 region, and the outside of the thigh. 



The genito-crural nerve, coming from the second and third lumbar 

 nerves, runs down upon the psoas muscle, and divides into a genital 

 and crural branch. The genital branch enters the internal abdominal 

 ring, and accompanies the spermatic cord, or round ligament, to the 

 integument of the groin ; the crural descends along the outer border 

 of tiie external iliac artery, enters the sheath of the femoral vessels, 

 and is distributed to the integument of the front of the thigh. 



The crural nerve, coming from the second, third, and fourth lumbar 

 nerves, is the largest branch of the lumbar plexus ; it pierces the 

 psoas muscle, then passes downward between it and the iliacus 

 internus muscle, and, about an inch below Poupart's ligament, divides 

 into numerous branches hereafter to be described, (p. 223.) 



The obturator nerre, coming from the third and fourth lumbar nerves, 

 pisses down among the fibres of the psoas muscle, and behind the iliac 

 vessels, along the brim of the pelvis to the upper and inner part of 

 the obturator foramen, which it perforates, to be distributed to the 

 adductor muscles of the thigh. An accessory obturator branch some- 

 times arises by separate filaments from the third and fourth lumbar 

 nerves, or from the upper part of the obturator nerve itself; it passes 

 down along the inner border of the psoas muscle, and is interesting 

 only because it supplies the hip-joint, which it enters beneath the 



