THE MALE REPRODUCTIVE ORGANS. 



221 



mented by connective tissue in forming the interalveolar partitions. 

 The layer of involuntary muscle surrounding the urethra is continu- 

 ous behind with the vesical sphincter, and in front with the muscular 

 envelope of the membranous portion of the canal. 



On either side of the urethral crest, which occupies the posterior 

 surface of the prostatic portion, a depression marks the position of 

 the prostatic fossa, into which open the orifices of the twelve to 

 twenty prostatic ducts. These recesses are lined with a continuation 

 of the stratified squamous epithelium which covers the adjacent 

 urethral mucous membrane ; these cells, however, are soon replaced 



FIG. 264. 



Section of human prostate more highly magnified : a, some of the tubular acini 

 lined with columnar cells ; b, muscular tissue of the intertubular septa. 



tvithin the ducts by others of the columnar type. As has already 

 been pointed out, the sinus pocularis, or uterus masculinus, 

 occupying the anterior part of the urethral crest, is to be regarded 

 as homologous with the cavity of the vagina and the uterus, the layer 

 of involuntary muscle belonging to the especial wall of the divertic- 

 ulum corresponding to the uterine muscular tissue, while the small 

 tubular glands present within the mucous membrane lining the sinus 

 are the homologues of those of the uterus. The prostate itself, 

 which is developed as a thickening of the urinary tract, cannot be 

 regarded in any sense as homologous with the uterus, notwithstand- 

 ing the apparently close relations with the sinus pocularis, since these 

 relations are secondary and attained in the course of its subsequent 

 growth. 



The blood-vessels of the prostate gland, branches of the adjacent 

 vesical, hemorrhoidal, and pudic arteries, pass into the interior of the 

 organ within the larger connective-tissue septa, where they break into 



