THE URINARY ORGANS. 207 



parts is thin, tolerably vascular, without glands or papilla, and 

 becoming very much thinner (0-005 — 0-0r"without epithelium), 

 is also continued upon the renal papillae, being likewise con- 

 nected with their interior stroma. Its epithelium, 0*02 — 0-04'" 

 thick, is laminated and characterised 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"' in length, and the superficial, rounded- 

 polygonal scales 0*006 — 0-04/" in size, or more flattened, and 

 reaching a diameter of 0-02'". The frequent occurrence of 

 two nuclei in these cells is a striking fact, as well as of clear 

 darkish-coloured round granules 0*001 — 0-002"' in size, which 

 often almost assume the aspect of nuclei. 



The urinary bladder, besides its peritoneal investment, 

 possesses the same membranes as the ureters. The muscular 

 coat presents, externally, the well-known longitudinal fibrous 

 layer {detrusor urince), with parallel bundles, from which iso- 

 lated fibres are continued upon the urachus ; beneath these 

 is a plexiform arrangement of oblique and transverse, stronger 

 and slenderer 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 vesicae). 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 contains 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 recognised as dark-bordered, fine 

 and medium-sized fibres, and is covered with a laminated epithe- 

 lium 0*03 — 0-05'" thick, whose deeper elements are usually fusi- 

 form, conical or cylindrical, the more superficial, rounded-poly- 

 gonal or flattened. They exhibit the same want of uniformity in 



