THE URINARY ORGANS. 271 



The function of the ureter is an active one. A few 

 drops of urine enter the ureter and are propelled 

 along by the peristaltic contraction of its muscula- 

 ture, which forces the urine in intermittent jets into 

 the bladder. In case of overdistention the force ex- 

 erted by this mechanism is sufficient to rupture the 

 bladder. In case of an obstruction in the ureter, 

 as in the passage of calculi, a violent contraction of 

 the smooth muscle follows, accompanied by severe 

 pains. In surgical operations ureters have been 

 sewed into the upper end of the bladder, or even into 

 the intestine. In the latter case the kidney usually 

 becomes infected with bacteria from the bowel. 



THE URINARY BLADDER. 



The urinary bladder is a receptacle for the reten- 

 tion of urine, with an average capacity of one pint, 

 although capable of much greater distention. When 

 empty it lies wholly within the pelvis, but if dis- 

 tended it rises into the abdomen. When moderately 

 filled it has a rounded form, but when completely 

 distended it becomes egg-shaped, the larger end, 

 called the base or fundus, being directed downward 

 and backward toward the rectum, and its smaller 

 end, the summit, resting against the anterior ab- 

 dominal wall. When distended the peritoneum 

 covers the bladder, excepting a triangular space of 

 two inches above the symphysis pubis known as the 

 space of Retzius. This is of surgical importance, 

 as the bladder can be opened through this space 

 without going through the peritoneum. 



The mucous membrane on the inner surface of the 



