PELVIS 573 



urethral orifice, semilunar or V-shaped in outline, with a 

 slightly elevated posterior lip which is known as the uvula 

 of the bladder (Figs. 224 and 225). The elevation indicates 

 the position of the middle lobe of the prostate gland below. 

 When the bladder is empty and contracted a number of radial 

 ridges of mucous membrane diverge from the margins of the 

 orifice. 



The ureteral orifices lie at the posterior angles of the 

 trigone. They are small semilunar slits, and are frequently 

 connected together by a transverse bar of mucous mem- 

 brane (torus vesicalis) which covers a bar of muscle. This 

 ridge is sometimes spoken of as Mercier's bar. Not 

 uncommonly a ridge of mucous membrane will be found 

 connecting each ureter with the urethra, and the muscular 

 bands which underlie the latter ridges are known as Bell's 

 muscles. Probes should be passed along the ureters to 

 demonstrate the obliquity with which the ducts pass through 

 the bladder wall. It will be found that each ureter runs 

 through the substance of the bladder wall for about three- 

 quarters of an inch (20 mm.). This arrangement serves the 

 purpose of a valve which allows urine to pass easily into the 

 bladder but tends to prevent its backward flow. When the 

 bladder is distended the openings of the ureters are about 

 an inch and a half apart (37 mm.), and about the same 

 distance from the orifice of the urethra, but when the viscus 

 is empty and contracted the distance between the orifices is 

 reduced to about one inch (25 mm.) in each case. 



The dissector should now investigate the relations of the 

 fundus of the bladder by palpation. Keeping one index finger 

 in the bladder and passing the other into the rectum, he will 

 find that he can distinguish the prostate below and around 

 the internal urethral orifice. Above the level of the prostate 

 he can feel the thick walls of the deferent ducts, one on 

 each side of the medial plane, and more laterally he will 

 recognise the convoluted coils of the seminal vesicles. If he 

 passes his finger upwards, along the median plane, he will 

 find that the deferent ducts diverge, and that between 

 them the rectum and bladder lie in contact. The area in 

 which this contact occurs corresponds with the posterior part 

 of the trigone, and varies considerably in size. When the 

 bladder is empty the area is small or absent, but it increases 

 considerably when the bladder is distended, and at one time 



