PHYSIOLOGICAL ANATOMY OF THE URINARY PASSAGES 333 



toneum. They have three distinct coats : an external coat, composed of 

 ordinary fibrous tissue with small elastic fibres ; a middle coat, composed 

 of non-striated muscular fibres ; and a mucous coat. 



The external coat requires no special description. It is prolonged 

 Into the calices and is continuous with the fibrous coat of the kidney. 



The fibres of the muscular coat, in the greatest part of the length 

 of the ureters, interlace with each other in every direction and are not 

 arranged in distinct layers ; but near the bladder, is an internal layer, 

 in which the direction of the fibres is longitudinal. 



The mucous lining is thin, smooth and without follicular glands. 

 It is thrown into narrow longitudinal folds, when the tube is flaccid, 

 which are easily effaced by distention. The epithelium exists in several 

 layers and is remarkable for the irregular shape of the cells. These 

 present, usually, dark granules and one or two clear nuclei with distinct 

 nucleoli. Some of the cells are flattened, some are rounded, and some 

 are caudate with one or two prolongations. 



Passing to the base of the bladder, the ureters become constricted, 

 penetrate the coats of this organ obliquely, their course in its walls 

 being a little less than an inch (25 millimeters) in length. This valvular 

 opening allows the free passage of the urine from the ureters, but com- 

 pression or distention of the bladder closes the orifices and opposes a 

 return of the liquid. 



The bladder, which serves as a reservoir for the urine, varies in its 

 relations to the pelvic and abdominal organs as it is empty or more or 

 less distended. When empty, it lies deeply in the pelvic cavity and is 

 then a small sac of an irregularly-triangular form. As it becomes filled, 

 it assumes a globular or ovoid form, rises up in the pelvic cavity, and 

 when excessively distended, it may extend partly into the abdomen. 

 When the urine is voided at normal intervals, the bladder, when filled, 

 contains about a pint (nearly 500 cubic centimeters) of liquid ; but under 

 pathological conditions it may become distended so as to contain ten or 

 twelve pints (about 4 or 5 liters), and in some instances of obstruction 

 it has been found to contain even more. The bladder usually is more 

 capacious in the female than in the male. 



The coats of the bladder are three in number. The external coat 

 is simply a reflection of the peritoneum, covering the posterior portion 

 completely, from the openings of the ureters to the summit, about one- 

 third of the lateral portion and a small part of the anterior portion. 



The middle or muscular coat consists of non-striated fibres, arranged 

 in three tolerably distinct layers : The external muscular layer is com- 

 posed of longitudinal fibres, which arise from parts adjacent to the 

 neck, and pass anteriorly, posteriorly and laterally over the organ, so 



