208 ANATOMY IN A NUTSHELL. 



LESSON LVI. 

 Lumbar Plexus. (Plates LXIII-LXXIII.) 



The lumbar plexus is made of the anterior branches of the first, second, 

 third, and a greater part of the fourth lumbar nerves. The twelfth dorsal 

 nerve scuds a communicating branch to the first lumbar nerve. This plexus 

 lies in the posterior pari of the Psoas magnus muscle in front of the transverse 

 processes of the lumbar vertebrae. 



The first lumbar nerve divides into two branches, the ilio-hypogastric and 

 the ilio-inguinal. (Plate LXX11I.) The ilio-hypogastric nerve passes through 

 the outer border of the Psoas magnus in front of the Quadratus iumborum and 

 behind the kidney and the large intestine. It pierces the Transversalis muscle 

 at the outer border of the Quadratus Iumborum to enter the areolar tissue be- 

 tween the transversalis muscle and the Internal oblique. At this point it fre- 

 quently joins the last dorsal and inguinal nerve. It divides into a hypogastric 

 branch and an iliac branch. The hypogastric branch passes between the Trans- 

 versalis and the Internal oblique muscles forward and downward and gives 

 branches to each of these muscles. It joins the ilio-inguinal nerve and pierces 

 the Internal oblique muscle near the anterior superior spine of the ilium and 

 passes beneath the aponeurosis of the External oblique towards the median line. 

 It pierces the aponeurosis of the External oblique muscle about an inch above 

 the externa] abdominal ring and .becomes cutaneous to supply the skin over the 

 symphysis. The iliac branch pierces both the Internal oblique muscle and the 

 Externa] oblique. The point where it pierces the External oblique muscle is 

 above the crest of the ilium a little in front of its middle portion. It supplies 

 the integument near the Gluteus medius muscle and the Tensor fascia femoris. 

 The ilio-inguinal nerve passes out of the Psoas magnus muscle a little below 

 the hypogastric, and thin crosses the Quadratus Iumborum to pass behind the 

 large intestine, after which it crosses the inner lip of the crest of the ilium pos- 

 teriorly. It now takes a forward course on the upper part of the Iliacus muscle 

 to pierce the Transversalis muscle near the anterior part of the crest of the ilium 

 where it communicates with the hypogastric branch of the ilio-hypogastric 

 nerve. It pass< s through the inguinal canal and gives a branch to the sper- 

 matic cord, and to the skin of the upper and middle part of the thigh and to 

 the scrotum and penis in the male, or to the mons veneris and the major lip in 

 1 1n' female. 



The second nerve of the lumbar plexus is the genito-crural, which conies 

 from the firsl and second lumbar nerves, mostly from the second. It passes 

 through the Psoas magnus muscle coming out on the anterior surface of this 

 muscle at the level of the lower border of the third lumbar vertebra. It now 

 passes downward on the outer side of the abdominal aorta and the common 

 iliac artery, then behind the meter where it divides into an external or genital 

 branch and an internal or crural branch. The EXTERNAL or GENITAL BRANCH 

 gives a branch to the external iliac artery ami it turns round the deep epigas- 

 tric artery at Poupart's ligament. It now enters the inguinal canal with the 

 spermatic cord in the male or the round ligament in the female. The Cremas- 



