THE UROGENITAL SYSTEM 



429 



as a reproductive outlet. Three portions of the urethra are recognized, 

 prostatic, membranous, and cavernous portions. (Fig. 352) 



The body of the penis consists of three masses of erectile tissue, 

 paired corpora cavernosa penis and the unpaired corpus cavemosum 

 urethrae. The latter enlarges at the root of the penis into a bulbus 

 urethrae and terminates at the extremity of the penis as a swollen mass 

 of erectile tissue, the glans penis. In its flaccid condition the glans is 

 covered by the foreskin or prepuce. The paired corpora cavernosa are 

 prolonged into the peritoneal region as far as the tuberosity of the ischium. 



Connective tissue, 



Epithelium. 





Red corpuscles in a 

 blood vessel. 





Smooth 

 muicle fibers. 



Fig. 353. — From a section of the prostate of a man twenty-three years old. The 

 epithelium is cut obliquely at x, and has artificially separated from the connective tissue 

 at XX. X360. (From Bremer's "Text Book of Histology.") 



In this way they form the fixed portion of the penis, the crura penis. 

 To each crus is attached an erector muscle, the ischio-cavemosus. 



The nerves of the penis are several. Branches of the second, third 

 and fourth sacral (spinal) nerves are known as erector nerves since their 

 stimulation causes the erection of the penis. Pressure upon the sym- 

 pathetic centers of the hypogastric plexus also stimulates erection. In a 

 flaccid penis the arterial blood supply is reduced through occlusion of the 

 lumen of the vessels by the contraction of local thickenings of their walls. 

 When, however, the artery is dilated, a free flow of blood into the venous 

 spaces of the corpora cavernosa causes them to become engorged with 

 blood and the penis consequently erected. 



