858 



THE NERVOUS SYSTEM. 



The posterior divisions of the two lower sacral nerves are situated below the 

 Multifidus spinse. They are of small size, and do not divide into internal and 

 external branches, but join with each other, and with the coccygeal nerve, so as 

 to form loops on the back of the sacrum, filaments from which supply the Extensor 

 coccygis and the integument over the coccyx. 



The coccygeal nerve divides into its anterior and posterior divisions in the spinal 

 caual. The posterior division is the smaller. It does not divide, but receives, as 

 already mentioned, a communicating branch from the last sacral, and is lost in the 

 fibrous structure on the back of the coccyx. 



The anterior divisions of the sacral nerves diminish in size from above down- 



Femoral a 



COCCYGEUS. 



Coccygeal. 

 Br. to 



LEVATOH AMI. SPH I NCTER AN I . 



FIG. 508. Side view of pelvis, showing sacral nerves. 



ward. The four upper ones emerge from the anterior sacral foramina : the ante- 

 rior division of the fifth, after emerging from the spinal canal through its termi- 

 nal opening, curves forward between the sacrum and the coccyx. All the anterior 

 sacral nerves communicate with the sacral ganglia of the sympathetic at their 

 exit from the sacral foramina. The first nerve, of large size, unites with the 

 lumbo-sacral cord, formed by the fifth lumbar, and a branch from the fourth lum- 

 bar. The second, equal in size to the preceding, and the third, about one-fourth 

 the size of the second, unite, together with a small fasciculus from the fourth, to 

 form the sacral plexus, a visceral branch being given off from the third nerve to 

 the bladder. 



The fourth anterior sacral nerve sends a branch to join the sacral plexus. The 

 remaining portion of the nerve divides into visceral and muscular branches, and 

 a communicating filament descends to join the fifth sacral nerve. The visceral 

 branches are distributed to the viscera of the pelvis, communicating with the 

 sympathetic nerve. These branches ascend upon the rectum and bladder, and 

 in the female upon the vagina, communicating with branches of the sympathetic 

 from the pelvic plexus. The muscular branches are distributed to the Levator 



