THE HUMAN PROSTATE GLAND 327 



eluded drawings, diagrams, and the construction of a wax model, 

 pictures of which are reproduced in this article. 



The bladder was distended upon fixation and the natural curve 

 at its neck mechanically straightened, so it is possible to get a 

 good idea of the thickness of its walls at various points. At the 

 place where the ureters join the vesical wall and begin their oblique 

 course through to its lumen, there is an increase in the size of 

 the base to twice that observed elsewhere in its circumference. 

 This increased thickness of the base is maintained throughout the 

 trigonal region, being most pronounced between the ureters where 

 the interureteric ridge is made up of fibers extending from one 

 ureteral wall mingling with those of the other. The trigone in 

 this as in the previously described cases is made up of muscular 

 fibers which originate in the walls of the ureters and pass over the 

 musculature proper of the bladder, becoming lost among the fibers 

 of the urethra. Just below the interureteric ridge the wall of the 

 base of the bladder becomes comparatively smaller, being very 

 little larger than the rest of the wall. As the sphincter is ap- 

 proached the entire vesical wall increases greatly in size, the base 

 always being considerably larger than any other part and the 

 trigonal fibers are always distinguishable from the tissue of the 

 vesical wall proper. The mucosa over the trigone is much more 

 richly supplied with blood vessels than any other portion. 



The internal sphincter is made up of circular fibers which are 

 very numerous at its upper part. It is larger at the floor of the 

 vesical cervix, and while many of the fibers pass entirely around 

 the orifice of the urethra the majority of them mingle with the 

 muscle bundles of the bladder on its ventral aspect which approach 

 much closer to the lumen of the orifice of the urethra here than in 

 the posterior wall. At the outermost portion of the sphincter 

 there is a great decrease in the number of fibers composing it and 

 it is about equal in size at all points of its circumference. In 

 its ventral portion a number of small longitudinally disposed 

 fibers are seen. The lower part of the sphincter ends considerably 

 outerward from the point where posterior lobe tubules have ex- 

 tended backward behind the two ejaculatory ducts. 



THE AMERICAN JOURNAL OF ANATOMY, VOL. 13, NO. 3 



