SECT. 189.] THE URINARY BLADDER. 415 



darkish contour, arc also found; these vary from o'ooi"' to 0-002'" 

 in size, and have often very much the appearance of nuclei 

 themselves. 



The urinary bladder is composed of layers similar to those of 

 the ureter, and receives, in addition, a covering from the peri- 

 toneum. The muscular coat is made up of an external longi- 

 tudinal layer, which is well known under the name of detrusor 

 urines. This layer is composed of parallel fasciculi, which are 

 provided with elastic tendons here and there (Treitz), and single 

 fibres are continued from these bundles upon the urachus. The 

 next layer of the muscular coat consists of a meshwork of fasciculi 

 of variable size, running obliquely and transversely, and matted 

 together ; at the neck of the bladder, these pass into a continuous 

 layer of circular fibres, the sphincter vesicce. A thick stratum of 

 yellowish-white fibres, situated immediately under the mucous 

 membrane of the fundus of the bladder, has received the name 

 corpus trigonum, and to this the so-called uvula vesicce (valv. 

 vesico-urethralis, Amussat), at the orifice of the urethra, is at- 

 tached. This corpus trigonum is connected with the longitudinal 

 muscular fibres of the ureters as they pass through the muscular 

 coat of the bladder; and it is composed of connective tissue, smooth 

 muscular fibres, and fine elastic elements; these last are mostly 

 longitudinal, but partly transverse in direction. V. Ellis calls 

 this stratum of fibres the submucous muscular stratum of the 

 bladder, and states that it extends upwards for some distance 

 above the trigonum. The mucous membrane of the bladder is 

 pale, smooth, and rather thick, with abundant submucous tissue 

 everywhere but at the trigonum ; this allows the mucous coat to 

 fall into numerous folds in the contracted state of the organ. The 

 membrane is destitute of villi ; it is well supplied with vessels, 

 especially at the fundus and neck. The nerves of the mucous 

 membrane are not very abundant, except at the base and cervix ; 

 they are dark-bordered fibres, fine and of medium thickness. — The 

 epithelium of the bladder measures from o , o3'" to o"05'" in thick- 

 ness, and is formed of cells arranged in laminae. The deeper cells 

 are spindle-shaped, conical, or cylindrical, while the more super- 

 ficial are roundish, polygonal, or flattened. In the irregularity of 

 their shape they rival the cells of the pelvic epithelium ; the more 

 superficial cells are frequently indented, to receive the ends of the 

 elongated ones below them, and peculiar stellate and toothed 

 shapes are thus produced. In the neck and fundus of the bladder 

 small glands are met with, either in the form of simple pyriform 



