THE HUMAN PROSTATE GLAND 333 



the size of the lumen and a few circularly arranged muscular fibers 

 are made out. 



By the sixteenth week there has been a very great develop- 

 ment of the musculature of the bladder, so that the fibers are 

 sharply defined from connective tissue. The muscle fibers form- 

 ing the trigonum vesicae are easily traced out into that structure 

 from the ureteral walls and the mucosa which is arranged in folds 

 everywhere else in this specimen is attached tightly to the tri- 

 gone and is smooth. The sphincter vesicae has become quite 

 sharply outlined by many muscular fibers arranged circularly at 

 the constricted lumen of the cervix. 



At the twentieth week the muscular fibers have become very 

 much more prominent but the most striking change is the enor- 

 mous increase in the size of and the number of fibers forming the 

 internal sphincter which seems to be tightly closing the vesical 

 orifice. The longitudinal fibers of the bladder intermingle with 

 the outermost of the fibers of the sphincter. The mucosa in this 

 stage is smooth over the trigonum vesicae and folded elsewhere. 



In the twenty-two weeks old fetus there is noted still greater 

 increase in the size of the bladder musculature and a marked in- 

 crease in the size of the interureteric bar. The trigone and the 

 bladder wall under it do not show the great increase in size over 

 the rest of the vesical wall observed in younger fetuses. The 

 fibers forming the trigone are observed to be more tightly bound 

 together than the fibers of the bladder wall and the mucosa is 

 smooth over it. The sphincter is large and closely bound to the 

 rest of bladder musculature. 



Further increase in the size of muscles forming the vesical wall, 

 trigonum and sphincter is noted at the thirtieth week and in the 

 bladder of the new-born. The sphincter in the latter is larger at 

 its upper margin than elsewhere and is very thick on its posterior 

 quadrant. Many of the fibers appearing there do not entirely 

 encircle the orifice but intermingle with longitudinally arranged 

 fibers from the anterior surface of the bladder. At the lower or 

 outermost part of the sphincter there are fewer fibers but they 

 all entirely encircle the orifice. 



