370 EXCRETION BY THE SKIN AND KIDNEYS. 



applied to the kidney at the hilum. The ureters themselves are membranous 

 tubes of about the diameter of a goose-quill, becoming much reduced in cali- 

 ber as they penetrate the coats of the bladder. They are sixteen to eighteen 

 inches (40 to 46 centimetres) in length, and pass from the kidneys to the 

 bladder, behind the peritoneum. 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 direc- 

 tion of the fibres is longitudinal. 



The mucous lining is thin, smooth and without any 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 

 granulations 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, pene- 

 trate the coats of this organ obliquely, their course in its walls being a little 

 less than an inch (25 mm.) in length. This valvular opening allows the 

 free passage of the urine from the ureters, but compression or distention of 

 the bladder closes the orifices and renders a return of the fluid impossible. 



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

 tions 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 c. c.) of liquid ; but under pathological conditions it may become dis- 

 tended so as to contain ten or twelve pints (about 4 or 5 litres), and in some 

 instances of obstruction it has been found to contain even more. The blad- 

 der is usually more capacious in the female than in the male. 



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

 ply 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 composed of 

 longitudinal fibres, which arise from parts adjacent to the neck, and pass 

 anteriorly, posteriorly and laterally over the organ, so that when they are 

 contracted they diminish its capacity chiefly by shortening its vertical diam- 

 eter. The fibres of the external layer are of a pinkish hue, being much more 



