THE SACRAL AND COCCYGEAL NERVES. 



789 



The three upper ones are covered, at their exit from the sacral canal, by the 

 Multifidus spinae, and divide into internal and external branches. 



The internal branches are small, and supply the Multifidus spinse. 



The external branches join with one another, and with the last lumbar and 

 fourth sacral nerves, in the form of loops on the posterior surface of the sacrum. 

 From these loops branches pass to the outer surface of the great sacro-sciatic 

 ligament, where they form a second series of loops beneath the Gluteus maximus. 

 Cutaneous branches from this second series of loops, usually two or three in 

 number, pierce the Gluteus maximus along a line drawn from the posterior 

 superior spine of the ilium to the tip of the coccyx. They supply the integument 

 over the posterior part of the gluteal region. 



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 

 canal. 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 

 integument over the back of the coccyx. 



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



Femoral a 



Br. to 



COCCYGEUS. 



Coccygeal. 

 ''Br. to' | Br. to 



LEVATOR ANI. SPHINCTER AMI. 



FIG. 421. 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- 



