454 THE URINARY SYSTEM 



THE MALE URETHRA 



The male urethra conducts the urine from the bladder to the sur- 

 face, its course being through the axis of the corpus spongiosum of the 

 penis (Fig. 446). It forms the terminal segment also of the genital 

 canal and conducts the semen; it accordingly performs a double func- 

 tion, serving both the urinary and the male reproductive system. The 

 character of its epithelium is variable, not only in its successive por- 

 tions, but it is also subject to great individual variation, and like that 

 of the bladder and ureter changes its appearance according as the canal 

 is collapsed or distended. In the first or prostatic portion of the urethra 

 the epithelium is of the transitional type ; in the membranous and penile 

 portion its superficial cells are elongated so that the epithelium usually 

 acquires a stratified columnar form; near the meatus the type is again 

 exchanged for a stratified squamous epithelium which is continuous 

 with that of the glans penis. 



The tunica jgropria of the urethra consists of^areolar_ti^ssue in which 

 are embedded the small branched tubulo-acinar urethral_^lands (of 

 Littre) lined by columnar, mucus-secreting cells. These glands are 

 more abundant along the upper surface. The mucosa also contains 

 frequent lacunar invaginations of the epithelium, and is thrown into 

 longitudinal rugae, its lumen being obliterated except when distended 

 by the passage of urine. 



The tunica propria, and especially that portion which is distant from 

 the urethral canal, is permeated by the thin-walled broad venous spaces 

 of the erectile tissue of the corpus spongiosum. The septa between 

 these venous spaces, in addition to the dense areolar tissue of which 

 they chiefly consist, contain many bundles of longitudinal smooth 

 muscle. In the deeper portions of the urethra circular muscle fibers 

 are also found in the outer part of this coat, and near the orifice of 

 the bladder they are somewhat thickened to form the sphincter urethrse 

 Moreover, the corpus spongiosum is invested with a thick sheath of 

 dense fibrous connective tissue. At the apex of the prostate circularly 

 disposed striped muscle fibers form a second urethral sphincter, the 

 external vesical sphincter. 



Nerve Supply. The nerve supply of the urethra includes both 

 sensory and motor spinal fibers, and sympathetic fibers for the smooth 

 muscle and the blood-vessels. 



