THE BLADDER. 



1909 



are distinguishable, the mucous, the submucous, the muscular, and the incomplete 

 serous. 



The miicous coat varies in thickness with both location and the degree of con- 

 traction. Over the vesical trigone, where always comparatively smooth, it is thin, 

 measuring only about . I mm. ; where strongly wrinkled by contraction, it may attain 

 a thickness of over 2 mm. The mucosa resembles closely that of the renal duct, 

 consisting of a fibre-elastic tunica propria covered with transitional epithelium. The 

 latter includes several strata of cells, the deepest of which are columnar, the middle 

 irregularly polygonal or club-shaped, and the inner plate-like, their deeper surface 

 fitting over and between the underlying elements. Although glands may be con- 

 sidered as absent, tubular depressions are occasionally found in the vicinity of the 

 trigone which are regarded by some (Kalischer, Brunn) as true glands. Waldeyer 

 has suggested that these structures may be interpreted as representing in a sense 

 urethral glands displaced during the development of the vesical trigone. 



The submucous coat, loose and elastic, permits free gliding of the mucous over 

 the muscular tunic when readjustment becomes necessary during contraction. Com- 

 posed of bundles of fibrous tissue interwoven with 'elastic fibres, it supports the 

 blood-vessels and nerve-plexuses, and contains numerous bundles of involuntary 

 muscle. It is not 



sharply defined 

 from the adjoin- 

 ing coats, but 

 blends with the 

 stroma of the mu- 

 cosa on the one 

 side and extends 

 between the 

 tracts of the mus- 

 cular coat on the 

 other. Beneath 

 the trigonum a 

 distinct submu- 

 cous layer is 

 wanting or re- 

 placed by a sheet 

 of muscular tis- 

 sue. 



The muscu- 

 lar coat, thicker 

 than the mucosa 

 and compara- 

 tively robust, va- 



FIG. 1624. 



Epithelium 



Mucous mem- 

 brane, thrown 

 into folds 



Section of wall of bladder, under very low magnification, 

 showing general disposition of coats. X 12. 



ries according to 



the condition of the bladder, being thin during distention and very thick in strong 

 contraction, when it may measure as much as 1.5 cm. The bundles of involuntary 

 muscle are arranged in two fairly distinct chief layers, a thin outer longitudinal and 

 a thick inner circular. Inside the latter, and virtually within the submucosa, lies an 

 incomplete additional layer. The longitudinal bundles, best developed on the upper 

 and lower surfaces, do not constitute a continuous sheet, but interlace, leaving inter- 

 fascicular intervals which are occupied by connective tissue. In the vicinity of the 

 prostate extensions of the outer layer are attached to the anterior pelvic wall as the 

 pubo-vesical muscles ; others pass backward to blend with the intestinal wall as the 

 recto-vesical muscles, while from the apex bundles are prolonged into the urachus. 

 The circular layer, although more robust and uniform than the outer, is weak and 

 imperfect over the trigonal region, and in both sexes is well developed only after 

 attaining the level of the internal ureteral orifices (Disse). Towards the apex of the 

 bladder the bundles of the circular layer assume an oblique and less regular dispo- 

 sition. The innermost layer that within the submucosa is represented by isolated 

 and indefinite muscular bundles that are blended with the connective tissue. Over 



