402 HEALTH AND DISEASE 



plexus. All the inferior branches of these nerves are connected with 

 the great sympathetic. 



Sacral Nerves, five pairs. — There are five sacral nerves. The 

 first four ^i'ls-^ out of the spinal canal by the sacral foramina, and the fifth 

 by the opening between the last sacral foramen and the first coccygeal 

 bone. After emerging from the spine, they each divide into a superior 

 and an inferior branch. The former of these pass upwards through the 

 supra-sacral openings, and are distributed to the muscles on the side of 

 the sacral spine and to the skin of the croup. The lower branches are 

 much the larger of the two, and pass in a direction downwards and back- 

 wards, to be distributed as follows :■ — The first and second, by joining with 

 the third, fourth and fifth lumbar, form the lumbo-sacral plexus. 



The third and fourth pass along the inner side, or even within the 

 texture of the sacro-sciatic ligament, and are joined together by a branch 

 going from one to the other. 



The third forms the internal pudic nerve, which winds round the 

 ischial arch, and with its fellow on the opposite side gains the dorsal 

 border of the penis, along which it runs, and ends in the mucous mem- 

 brane covering the glans penis. In its course from behind forward it gives 

 numerous branches to the corpora cavernosa and the urethral canal, and 

 while in the pelvis, two small ramuscules go to the perineal region, and 

 heemorrhoidal branches to the anus. 



The fourth, together with a branch of the third, innervates the sphincter 

 muscle of the anus and surrounding skin, and the fifth, after giving a 

 branch to the first coccygeal nerve, is expended in the muscles and in- 

 tegument about the base of the tail and the root of the penis. 



Coccygeal Nerves. — These number five or six pairs, which decrease 

 in volume from the first to the last. The first coccygeal communicates 

 with the last sacral nerve, and then with others passes backwards, and 

 is expended in the muscles and skin of the tail. 



LUMBO-SACKAL PLEXUS 



This is a combination of nerves for the supply of the hind-limb. It 

 corresponds with the brachial plexus of the fore-limb in being formed by the 

 inferior branches of the fourth, fifth, and sixth lumbar, and the first and 

 second sacral nerves. 



The branches given off" from this plexus are as follow: — 



1. Iliaco-Muscular Branches. — Small branches given to the psoas 

 magnus, psoas parvus, and iliacus muscles. 



2. Anterior or Great Crural Nerve. — This is a nerve of considerable 



