LUMBAR PLEXUS. 469 



pass backwards between the transverse processes of the corresponding 

 vertebrae, and each nerve divides into an internal and an external 

 branch. The internal branch, the smaller of the two, passes inwards 

 to be distributed to the multifidus spinae and interspinales, and be- 

 coming cutaneous supplies the integument of the lumbar region on the 

 middle line. The external branches communicate with each other by 

 several loops, and, after supplying the deeper muscles, pierce the sacro- 

 lumbalis to reach the integument to which they are distributed. The 

 external branches of the three lower lumbar nerves (nervi clunium su- 

 periores postici) descend over the posterior part of the crest of the 

 ilium, and are distributed to the integument of the gluteal region. 



LUMBAR PLEXUS. 



The Lumbar plexus is formed by the communications and anasto- 

 moses which take place between the anterior branches of the five lum- 

 bar nerves, and between the latter and the last dorsal. It is narrow 

 above and increases in breadth inferiorly, and is situated between the 

 transverse processes of the lumbar vertebrae and the quadratus lumbo- 

 ruin behind, and the psoas magnus muscle in front. 



The Branches of the lumbar plexus are the 



Musculo-cutaneous , 



External-cutaneous, 



Genito-crural, 



Crural, 



Obturator, 



Lumbo- sacral. 



The MUSCULO-CUTANEOUS NERVES, two in number, superior and 

 inferior, proceed from the first lumbar nerve. The superior musculo- 

 cutaneous nerve (ilio-scrotal, ilio-hypogastricus), passes outwards be- 

 tween the posterior fibres of the psoas magnus, and crossing obliquely 

 the quadratus lumborum to the middle of the crest of the ilium, pierces 

 the transversalis muscle, and gives off a cutaneous branch. It then 

 winds along the crest of the ilium between the transversalis and inter- 

 nal oblique, and divides into two branches, abdominal and scrotal. 

 The abdominal branch is continued forwards parallel with the last in- 

 tercostal nerve to near the rectus muscle, to which it sends branches 

 and perforates the aponeuroses of the internal and external oblique to 

 be distributed to the integument of the mons pubis and groin. The 

 scrotal branch-, opposite the anterior superior spinous process of the ilium, 

 communicates with the inferior musculo-cutaneous nerve, and passes 

 forward to the external abdominal ring. It then pierces the cremaster 

 muscle and accompanies the spermatic cord in the male, and the round 

 ligament in the female, to be distributed to the integument of the 

 scrotum or external labimn. The inferior musculo-cutaneous nerve 



