THE URINARY ORGANS. 607 



190. Excretory urinary passages. The ureters, the pelvis, and 

 calices of the kidney, are all composed of an external fibrous membrane, 

 a smooth muscular layer, and a mucous membrane. The first, formed 

 of common connective tissue and elastic fibres, chiefly of the finer kind, 

 is continuous, at the point where the calices surround the papilla?, with 

 the fibrous tunic of the kidney. The muscular layer in the ureters is 

 very distinct, with external, longitudinal, and internal transverse fibres, 

 to which, towards the bladder, internal longitudinal fibres also are 

 supcradded. In the pelvis of the kidney the two muscular layers are 

 quite as thick as in the ureter, whilst in the calices they become thinner 

 and thinner, ceasing where the latter are inserted into the papilla. 

 The mucous membrane of all these parts is thin, tolerably vascular, 

 without glands or papilla*, and becoming very much thinner (O'005-O'Ol 

 of a line, without epithelium), is also continued upon the renal papilla), 

 being likewise connected with their interior stroma. Its epithelium, 

 0-02-0-04 of a line thick, is laminated and characterized by the variety 

 of form and size of its elements, of which the most deeply-seated cells 

 are rounded and small, those in the middle cylindrical or conical, 0-01- 

 0-02 of a line in length, and the superficial, rounded-polygonal scales 

 0-006-0-04 of a line in size, or more flattened, and reaching a diameter 

 of 0-02 of a line. The frequent occurrence of two nuclei in these cells 

 is a striking fact, as well as of clear, darkish-colored round granules 

 0-001-0*002 of a line in size, which often almost assume the aspect of 

 nuclei. 



The urinary bladder, besides its peritoneal investment, possesses the 

 same membrane as the ureters. The muscular coat presents, exter- 

 nally, the well-known longitudinal fibrous layer (detrusor urinal), with 

 parallel bundles, from which isolated fibres are continued upon the 

 urachus ; beneath these is a plexiform arrangement of oblique and 

 transverse, stronger and slender fasciculi, interwoven into a true plexus, 

 which do not completely cover the entire mucous membrane, and, at the 

 neck of the bladder, constitute a strong continuous circular fibrous layer 

 (sphincter vesicce). The corpus trigonum, in the fundus of the bladder, 

 is a thick layer of whitish-yellow fibres, lying immediately beneath the 

 mucous membrane, continuous with the longitudinal muscular fibres of 

 the ureters passing through the muscular coat of the bladder, and con- 

 tains chiefly longitudinal, but also some transverse fine elastic elements, 

 connective tissue, and smooth muscular fibres. The mucous membrane, 

 pale, smooth, and tolerably thick, except where the corpus trigonum is 

 situated, presents an abundant submucous layer, and consequently, when 

 the bladder contracts, is thrown into numerous folds. It presents no 

 villi, is tolerably rich in vessels, especially at the fundus and neck, less 

 so in nerves, which, however, especially in those two situations where 

 they are more abundant, may be recognized as dark-bordered, fine and 



