LUMBAR NERVES. 519 



The first lumbar nerves arise from the medulla spinalis, before 

 it forms the cauda equina ; the other four pair are formed by the 

 cauda equina. ^ 



They commence from the medulla by anterior and posterior 

 fasciculi, which are united just beyond the ganglion formed on 

 the posterior root. From this union anterior and posterior 

 branches go off, which are very different in size, the anterior 

 being the largest. 



The posterior branches are distributed to the muscles of the 

 back. The anterior send branches to the ganglions of the sym- 

 pathetic nerve, and also communicate with each other to form 

 the Lumbar Plexus, which is situated on the lateral parts of the 

 bodies of the lumbar vertebrae, before their transverse processes, 

 and supplies nerves to the muscles of the thigh. 



The First Lumbar Nerve 



Is connected, by its anterior branch, to the last dorsal and the 



second lumbar. From the same branch two ramifications go off 



to the Quadratus Lumborum, and obliquely across that muscle, 



'to the lower part of the abdominal muscles near the spine of the 



ilium. 



These are called the superior and inferior musculo-cutaneous, 

 external spermatic, or ilio-scrotal nerves. The superior traverses 

 the transversalis muscle near the crest of the ilium, and divides 

 into two branches. One called the abdominal, passes across the 

 abdomen to the rectus muscle, to which and the integument 

 covering it, it is distributed ; the other branch named scrotal, 

 passes out at the external abdominal ring, and is distributed to 

 the skin of the groin and that covering the os pubis, to the scro- 

 tum of the male, and the labium externum of the female. The 

 inferior musculo-cutaneous is smaller than the superior, but has 

 nearly a similar distribution : it anastomoses with the latter near 

 the anterior superior spine of the ilium. 



The Second Lumbar Nerve, 



Sends off a branch called the External Cutaneous, which 

 perforates the outer border of the psoas near its middle, crosses 



