668 THE SACRAL NERVES. 



ANTERIOR PRIMARY DIVISIONS OF THE SACRAL AND 

 COCCYGEAL NERVES. 



THE SACRAL 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 the 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 

 plexus. 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 which they 

 give rise are described. 



THE FOURTH SACRAL NERVE. 



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

 plexus ; the remainder, which is nearly half the nerve, supplies branches to 

 the viscera and muscles of the pelvis, and sends downwards a connecting 

 filament to the fifth nerve. 



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

 lower part of the bladder, and communicate freely with branches from the sympa- 

 thetic nerve. Offsets are distributed to the neighbouring viscera, according to 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 fourth, and not unfrequently from both of these nerves. 



(b) Of the muscular branches, one supplies the levator ani, piercing that muscle 

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

 sphincter muscle of the rectum. The last branch, after passing either through the 

 coccygeus, or between it and the levator ani, reaches the perinaeum, 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 pelvis) 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 spinal 



