608 THE SACRAL AND COCCYGEAL NERVES. 



SACRAL AND COCCYGEAL NERVES. 



The anterior divisions of the first four sacral nerves emerge from the 

 spinal canal by the anterior sacral foramina, and the fifth passes out 

 between the sacrum and coccyx. 



The first two sacral nerves are large, and of nearly equal size ; the 

 others diminish rapidly, and the fifth is exceedingly slender. Like the 

 anterior divisions of tiie other spinal nerves, those of the sacral nerves 

 communicate with the sympathetic : the communicating cords are very 

 short, as the sympathetic ganglia are close to the inner margin of the 

 foramina of the sacrum. 



The first three nerves and part of the fourth contribute to form the 

 sacral ]5lexus. The fifth has no share in the plexus, — it ends on the 

 back of the coccyx. As the description of the fourth and fifth sacral 

 nerves and of the coccygeal will occupy only a short space, these three 

 nerves may be noticed first, before the other nerves and the numerous 

 branches to whicli they give rise are described, 



'x'hb fourth saceal nerve. 



Only one pare of the anterior division of this nerve joins the sacral 

 plexus ; the remainder, which i.s nearly half the nerve, supplies branches 

 to the viscera and muscles of the pelvis, and sends downwards a con- 

 necting filament to the fifth nerve. 



(a) The visceral hranclirs of the fourth sacral nerve are directed forwards to 

 the lower pai-t of the bladder, and communicate freely with branches from the 

 sympathetic nerve. Offsets are distributed to the neighbouring viscera, accord- 

 ing ^0 the sex. They will be described with the pelvic portion of the sympathetic 

 nerve. The foregoing branches are, in some instances, furnished by the third 

 sacral nerve instead of the fouith, and not unfrequently from both of these 

 nerves. 



(5) Of the muscular brancTws, one supplies the levator ani. piercing that muscle 

 on the pelvic surface ; another enters the coccyrjevs, whilst a third ends in 

 the external spJtincter miiscle of the rectum. The last branch, after passing 

 either through the coccygeus, or between it and the levator ani, reaches the 

 perinfeum, and is distributed likewise to the integuments between the anus and 

 the coccyx. 



THE FIFTH SACRAL NERVE, 



The anterior branch of this, the lowest sacral nerve, comes forwards 

 through the coccygeus muscle opposite the junction of the sacrum with 

 the first coccygeal vertebra ; it then descends upon the coccygeus nearly 

 to the tip of the coccyx, where it turns backwards through the fibres 

 of that muscle, and ends in the integument upon the posterior and 

 lateral aspect of the bone. 



As soon as this nerve appears in front of the bone (in the peh'is) it is joined 

 by the descending filament from the fourth nerve, and lower down by the small 

 anterior division of the coccygeal nerve. It supplies small filaments to the 

 coccygeus muscle. 



THE COCCYGEAL NERVE, 



The anterior branch of the coccygeal, or, as it is sometimes named, 

 the sixth sacral nerve, is a very small filament. It escapes from the 



