THE PERINEUM, MALE. 411 



Nerve Supply. Perineal. 



Action. The anterior portion compresses the dorsal vein 

 of the penis and so produces erection of the organ. The 

 middle portion compresses the bulb and its vessels and so 

 aids the action of the anterior portion. The posterior part 

 compresses the membranous urethra and expels its contents 

 (urine or semen). This last action is continued by the two 

 other portions of the muscle, acting peristaltically from be- 

 hind forward. 



The Internal Pudic Artery. Figs. 82, 83, 1 12, 1 14. 



This is the smaller branch of the bifurcation of the 

 anterior trunk of the internal iliac artery, the larger being 

 the sciatic. It leaves the pelvic cavity with the sciatic be- 

 tween the coccygeus and pyriformis muscles, through the 

 greater sacrosciatic foramen, curves around the base of the 

 spine of the ischium, having the internal pudic nerve on its 

 internal and the nerve to the obturator internus muscle on 

 its external side ; then re-enters the pelvic cavity (ischio- 

 rectal fossa) through the lesser sacrosciatic foramen ; the 

 artery now runs forward along the outer surface of the 

 ischiorectal fossa, being contained in a canal (Alcock's) 

 formed by the separation of the obturator fascia. In this 

 part of its course the artery is situated about an inch 

 above the lower margin of the tuberosity of the ischium, 

 and is accompanied by the pudic nerve, which divides soon 

 after entering the ischiorectal fossa into the superficial peri- 

 neal nerve and the dorsal nerve of the penis ; the former 

 nerve is below and the latter above the artery (subject 

 standing). 



The artery continues forward, perforates the posterior 

 layer of the triangular ligament close to the ramus of the 

 ischium, along which it extends between the two layers of 



