MICTURITION 207 



of causing regurgitation into the ureter. The ureter is com- 

 posed of three coats. The outer is fibrous, the middle muscular, 

 and the internal mucous. 



The bladder serves as a reservoir for the urine until such time 

 as it is convenient for it to be evacuated. This organ, when 

 empty, lies deep in the pelvis in front of the rectum in the male 

 and of the uterus in the female. When moderately distended 

 it will hold about a pint, has an ovoid shape and rises to the 

 brim of the pelvis. It also has three coats. The outer is perit- 

 oneal, and covers the posterior and small parts of the lateral 

 and anterior surfaces only. Its lower limit posteriorly is the 

 entrance of the ureters. The middle layer is muscular. The 

 fibers, which are non-striped, are disposed in three sheets. Their 

 contraction compresses the contents from all directions. Em- 

 bracing the neck (outlet) of the bladder is a thick band of plain 

 muscle tissue known as the sphincter vesicce. The tonic contrac- 

 tion of this muscle prevents the continual escape of urine. The 

 inner coat of the bladder is mucous. It is rather thick, and 

 loosely adherent to the subjacent muscular coat except over the 

 corpus trigonum where it is closely attached. The corpus trigo- 

 num is a triangular body of fibrous tissue just underneath the 

 mucous membrane; its apex is at the origin of the urethra, and 

 its other angles are at the vesical openings of the ureters. 



Absorption from the intact mucous membrane of the bladder 

 takes place very sparingly, if at all. Abrasions of the membrane 

 from any cause allow absorption to occur; and this fact may be 

 made use of to locate lesions giving rise to hematuria. Iodide 

 of potassium injected into the bladder can be detected in the 

 saliva if the bladder is the source of the blood. 



Micturition. When the bladder has become moderately full 

 the desire to expel its contents arises. The act of micturition 

 involves relaxation of the sphincter vesicce and contraction of the 

 muscular walls of thejbladder aided by the abdominal muscles 

 and those of the urethra. A slight contraction of the abdominal 



