THE PUDENDAL PLEXUS 1017 



range of variation and the common method of formation of the large nerve of this 

 plexus in each of the three classes. 



COMPOSITION OF THE NERVES OF THE PUDENDAL PLEXUS 



Range of Variation 



Nerve. Proximal. Ordinary. Distal. 



Pudic nerve 1,2,3,4,5 8. 1,2,3,4 8. 2,3,4,5 8. 



Common Composition 

 Nerve. Proximal. Ordinary. Distal. 



Pudic nerve 2,3 8. 2,3,4 8. 3,4 8. 



The pudendal plexus is commonly formed by parts of the anterior divisions of 

 the second, third, and fourth sacral nerves. It lies in the lower part of the back 

 of the pelvis, and gives off visceral, muscular, and terminal branches. 



Visceral branches (pelvic splanchnics) arise from the third and fourth sacral 

 nerves especially, and enter branches of the sympathetic plexus. They are 

 distributed both directly (their afferent or sensory fibres terminating in the pelvic 

 viscera) and by their visceral efferent fibres terminating in the ganglia of the 

 sympathetic plexus to the pelvic viscera (figs. 765, 791). The middle haemor- 

 rhoidal nerves pass to the rectum, the inferior vesical nerves to the bladder, and, 

 in the female, the vaginal nerves to the vagina fsee Sympathetic System). 



Muscular branches are given by the fourth sacral nerve to the coccygeus, 

 levator ani, and sphincter ani externus (fig. 765). 



The nerves to the two former muscles pass into the pelvic surfaces of the muscles, but that 

 to the last-named muscle, called the perineal branch, passes backward between the levator 

 ani and the coccygeus, or through the posterior fibres of the latter muscle, into the posterior 

 part of the ischio-rectal fossa, and, in addition to supplying the sphincter ani, it gives cutaneous 

 filaments to the skin between the anus and the coccyx. 



Terminal branches. — The pudic nerve [n. pudendus] rises usually from the 

 anterior primary divisions of the second, third, and fourth sacral nerves (fig. 765). 

 It emerges from the pelvis below the piriformis, crosses the spine of the ischium, 

 lying to the medial side of the internal pudic artery (fig. 769), and accompanies 

 the artery, through the small sciatic foramen, into Alcock's canal in the ob- 

 turator fascia on the lateral wall of the ischio-rectal fossa, where it terminates by 

 dividing into three branches, the inferior hsemorrhoidal, the perineal, and the 

 dorsal nerve of the penis. 



The inferior haemorrhoidal nerves frequently arise independently from the 

 third and fourth sacral nerves, pierce the medial wall of Alcock's canal, and pass 

 forward and medialward through the ischio-rectal fat to supply the sphincter ani 

 externus and adjacent skin. They anastomose with branches of the perineal 

 nerve. 



The perineal nerve runs forward for a short distance in Alcock's canal and 

 divides into a deep and a superficial branch. The deep branch breaks up into 

 filaments, one or two of which pierce the medial wall of the canal and pass 

 medialward to the anterior fibres of the sphincter and levator ani. The re- 

 maining part of the nerve pierces the base of the uro-genital trigone (triangular 

 ligament), and enters the superficial pouch of the urethral triangle, where it is 

 distributed to the bulb of the urethra, and to the transversus perinei, bulbocaver- 

 nosus, and ischiocavernosus. It also sends some sensory filaments to the mucous 

 membrane of the urethra. The superficial branch almost at once divides into 

 medial and lateral branches, the posterior scrotal (labial) nerves. 



Both branches pass through the wall of Alcock's canal into the anterior part of the ischio- 

 rectal fossa, then they pierce the base of the uro-genital trigone, and enter the superficial pouch 

 of the urethral triangle. The lateral branch usually passes below the transversus perinei, 

 and the medial branch above the muscle or through its fibres. The lateral branch connects 

 with the long pudendal nerve, and with the inferior hsemorrhoidal nerve, and both branches 

 end in terminal filaments which anastomose and which are distributed to the skin of the scrotum 

 and the anterior part of the perineum in the male, and to the labium majus in the female. 



