218 



NORMAL HISTOLOGY. 



fibres, and supports the blood-vessels and nerve-plexuses, and occasionally 

 contains small lymph-nodules. The submucosa is not sharply defined from 

 the adjacent coats, but blends with the tunica propria on the one side and 

 penetrates between the tracts of muscle-bundles on the other. Beneath the 

 trigonum a distinct submucous layer is wanting, or replaced by a sheet of 

 muscular tissue. 



The muscular coat, thicker than the mucous and comparatively 

 robust, varies according to the condition of the bladder, being thin during 

 distention and very thick during strong contraction, when it may measure 

 as much as 1.5 cm. The bundles of involuntary muscle are arranged as two 

 fairly distinct chief layers a thick circular and a thin outer longitudinal. 

 Inside the circular, virtually within the mucosa, lies an incomplete additional 



Epithelium 



Mucous mem- 

 brane, thrown- 

 into folds 



Obliquely cut 

 longitudinal 

 bundles 



Fibrous coat 



FIG. 269. Section of wall of bladder, showing general disposition of coats. X 12. 



layer of mostly oblique bundles. The longitudinal bundles, best developed 

 on the upper and lower surfaces of the bladder, do not form a continuous 

 sheet but interlace, leaving intervals occupied by connective tissue. The 

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

 weak and imperfect over the trigonal region and is well developed only 

 above the level of the orifices of the ureters, towards the apex of the 

 bladder becoming oblique and less regular. The innermost layer, largely 

 represented by isolated and indefinite bundles intermingled with connective 

 tissue, is condensed over the trigone, where it exists as a compact muscular 

 sheet closely united with the overlying mucous membrane, and surrounds 

 the orifices of the ureters and of the urethra with sphincter-like bands. 



The fibrous coat, composed of fibro-elastic bundles, is blended over 

 the upper and lateral surfaces of the bladder with the serous (peritoneal) 

 covering; where this is wanting, it is continuous with the areolar tissue con- 

 necting the bladder with the surrounding pelvic wall and organs. It is 

 strongest over the inferior surface, where it receives additions from the 

 pelvic fascia, while towards the apex and beneath the peritoneum it is less 

 definite and intermingled with adipose tissue. 



