90S NEUROLOGY 



fossa, being contained in a sheath of the obturator fascia termed Alcock's canal, 

 and divides into two terminal branches, viz., the perineal nerve, and the dorsal nerve 

 of the penis or clitoris. Before its division it gives off the inferior hemorrhoidal nerve. 



The inferior hemorrhoidal nerve (n. haemorrhoidalis inferior] occasionally arises 

 directly from the sacral plexus; it crosses the ischiorectal fossa, with the inferior 

 hemorrhoidal vessels, toward the anal canal and the lower end of the rectum, 

 and is distributed to the Sphincter ani externus and to the integument around the 

 anus. Branches of this nerve communicate with the perineal branch of the posterior 

 femoral cutaneous and with the posterior scrotal nerves at the forepart of 

 the perineum. 



The perineal nerve (n. perinei), the inferior and larger of the two terminal branches 

 of the pudendal, is situated below the internal pudendal artery. It accpmpanies 

 the perineal artery and divides into posterior scrotal (or labial) and muscular branches. 



The posterior scrotal (or labial) branches (nn. scrotales (or labiales) posteriores; 

 superficial peroneal nerves} are two in number, medial and lateral. They pierce 

 the fascia of the urogenital diaphragm, and run forward along the lateral part of 

 the urethral triangle in company with the posterior scrotal branches of the perineal 

 artery; they are distributed to the skin of the scrotum and communicate with the 

 perineal branch of the posterior femoral cutaneous nerve. These nerves supply the 

 labium majus in the female. 



The muscular branches are distributed to the Transversus perinsei superficialis, 

 Bulbocavernous, Ischiocavernosus, and Constrictor urethrae. A branch, the 

 nerve to the bulb, given off from the nerve to the Bulbocavernosus, pierces this 

 muscle, and supplies the corpus cavernosum urethrae, ending in the mucous 

 membrane of the urethra. 



The dorsal nerve of the penis (n. dorsalis penis') is the deepest division of the puden- 

 dal nerve; it accompanies the internal pudendal artery along the ramus of the 

 ischium; it then runs forward along the margin of the inferior ramus of the pubis, 

 between the superior and inferior layers of the fascia of the urogenital diaphragm. 

 Piercing the inferior layer it gives a branch to the corpus cavernosum penis, and 

 passes forward, in company with the dorsal artery of the penis, between the layers 

 of the suspensory ligament, on to the dorsum of the penis, and ends on the glans 

 penis. In the female this nerve is very small, and supplies the clitoris (n. dorsalis 

 clitoridis}. 



The Visceral Branches arise from the third and fourth, and sometimes from the 

 second, sacral nerves, and are distributed to the bladder and rectum and, in the 

 female, to the vagina; they communicate with the pelvic plexuses of the sympathetic. 



The Muscular Branches are derived from the fourth sacral, and supply the Levator 

 ani, Coccygeus, and Sphincter ani externus. The branches to the Levator ani 

 and Coccygeus enter their pelvic surfaces; that to the Sphincter ani externus 

 (perineal branch) reaches the ischiorectal fossa by piercing the Coccygeus or by 

 passing between it and the Levator ani. Cutaneous filaments from this branch 

 supply the skin between the anus and the coccyx. 



Anococcygeal Nerves (nn. anococcygei) . The fifth sacral nerve receives a com- 

 municating filament from the fourth, and unites with the coccygeal nerve to form 

 the coccygeal plexus. From this plexus the anococcygeal nerves take origin; they 

 consist of a few fine filaments which pierce the sacrotuberous ligament to supply 

 the skin in the region of the coccyx. 



THE SYMPATHETIC NERVOUS SYSTEM. 



The sympathetic nervous system (Fig. 838) innervates all the smooth muscles and 

 the various glands of the body, and the striated muscle of the heart. The efferent 

 sympathetic fibers which leave the central nervous system in connection with 



