THE URINARY BLADDER 1365 



peritoneal fold over each impervious hypogastric artery is called the plica umbili- 

 calis lateralis (Fig. 978), and is the prolongation forward of the ligamentum umbil- 

 icale laterale. Besides the true and false ligaments, the bladder receives support 

 from the fibrous tissue and unstriated muscle about the seminal vesicles, and ter- 

 minations of the ureters and vasa deferentia. In the female the connection with 

 the anterior vaginal wall supports the base of the bladder. In both sexes the most 

 solidly fixed part of the bladder is about the orifice of the urethra. 



Structure. The bladder is composed of three coats fibrous, muscular, and mucous. 



The fibrous coat (tunica fibrosa) consists of white fibrous tissue, which supports the other 

 coats. It is partially invested by peritoneum. 



The muscular coat (tunica muscularis} (Figs. 1112, 1113, and 1114) consists of three incom- 

 pletely differentiated layers of unstriped muscular fibre an external layer, composed of fibres 

 having for the most part a longitudinal arrangement; a middle layer, in which the fibres are 

 arranged, more or less, in a circular manner; and an internal layer, in which the fibres have a 

 general longitudinal arrangement. 



The fibres of the external longitudinal layer (stratum cxternum) arise from the posterior sur- 

 face of the body of the os pubis in both sexes (TO. pubovesicalis) , and in the male arise also from 

 the adjacent part of the prostate gland and its capsule. They pass, in a more or less longitudinal 

 manner, up the anterior surface of the bladder, over its apex, and then descend along its pos- 

 terior surface to its base, where they become attached to the prostate in the male and to the front 

 of the vagina in the female. At the sides of the bladder the fibres are arranged obliquely and 

 intersect one another. The external longitudinal layer has been named the Detrusor urinse 

 muscle. 



The middle circular layers (stratum medium) are very thinly and irregularly scattered on the 

 body of the organ, and, though to some extent placed transversely to the long axis of the 

 bladder, are for the most part arranged obliquely. Toward the lower part of the bladder, 

 around the neck and the commencement of the urethra, they are disposed in a thick circular 

 layer, forming the sphincter vesicae, which is continuous with the muscle fibres of the prostate 

 gland. 



The internal longitudinal layer (stratum internum} is thin, and its fasciculi have a reticular 

 arrangement, but with a tendency to assume for the most part a longitudinal direction. Two 

 bands of oblique fibres, originating behind the orifices of the ureters, converge to the back part 

 of the prostate gland, and are inserted, by means of a fibrous process, into the so-called middle 

 lobe of that organ. They are the muscles of the ureters, described by Sir C. Bell, who supposed 

 that during the contraction of the bladder they served to retain the oblique direction of the ureters, 

 and so prevent the reflux of the urine into them. 



FIG. 1115. Superficial layer of the epithelium of FIG. 1116. Deep layers of epithelium of bladder, 



the bladder. Composed of polyhedral cells of vari- showing large club-shaped cells above, and smaller, 



ous sizes, each with one, two, or three nuciei. (Klein more spindle-shaped cells below, each with an oval 



and Noble Smith.) nucleus. (Klein and Noble Smith.) 



The mucous coat (tunica mucosa} is thin, smooth, and of a pale rose color. It is continuous 

 above through the ureters with the lining membrane of the uriniferous tubes, and below with 

 that of the urethra. Except at the trigone, it is connected very loosely to the muscular coat by a 

 layer of areolar tissue, and is therefore thrown into folds or rugae when the bladder is empty (Fig. 

 1118). The epithelial covering it is of the transitional variety, consisting of a superficial layer 

 of polyhedral flattened cells, each with one, two, or three nuclei (Fig. 1 1 15) ; beneath these is a 

 stratum of large club-shaped cells with the narrow extremity of each cell directed downward and 

 wedged in between smaller spindle-shaped cells, each with an oval nucleus (Fig. 1116). There 

 are no true glands in the mucous membrane of the bladder, though certain mucous follicles 



