336 THE ORGANS 



delicate fibrous tissue containing few elastic fibrils and rich in cells 

 (Fig. 231, cli). Diffuse lymphatic tissue frequently occurs in the 

 stroma, especially of the pelvis. Occasionally the lymphatic tissue 

 takes the form of small nodules. Mucous glands in small numbers 

 are found in the stroma of the pelvis and upper part of the ureter. 

 There is no distinct submucosa, although the outer part of the 

 stroma is sometimes referred to as such. 



The muscularis consists of an inner longitudinal and an outer 

 circular layer (Fig. 231, cml and cmc). In the lower part of the 

 ureter a discontinuous outer longitudinal layer is added. 



The fibrosa consists of loosely arranged connective tissue and 

 contains many large blood-vessels. It is not sharply limited exter- 

 nally, but blends with the connective tissue of surrounding structures, 

 and serves to attach the ureter to the latter (Fig. 231, ad). 



The larger blood-vessels run in the fibrous coat. From these, 

 branches pierce the muscular layer, give rise to a capillary network 

 among the muscle cells, and then pass to the mucosa, in the stroma 

 of which they break up into a rich network of capillaries. The veins 

 follow the arteries. 



The lymphatics follow the blood-vessels, being especially numer- 

 ous in the stroma of the mucosa. 



Nerves. — Plexuses of both medullated and non-medullated fibres 

 occur in the walls of the ureter and pelvis. The non-medullated 

 fibres pass mainly to the cells of the muscularis. Medullated fibres 

 enter the mucosa w^here they lose their medullary sheaths. Terminals 

 of these fibres have been traced to the lining epithelium. 



The Urinary Bladder 



The walls of the bladder are similar in structure to those of the 

 ureter. 



The mucous membrane is thrown up into folds or is compara- 

 tively smooth, according to the degree of distention of the organ. 

 The epithelium is of the same general type — transitional epithelium 

 (seepage 77) — as that of the ureter. The number of layers of cells 

 and the shapes of the cells depend largely upon whether the bladder 

 is full or empty. In the collapsed organ the superficial cells are 

 cuboidal or even columnar, their under surfaces being marked by 

 pit-like depressions caused by pressure of underlying cells. Beneath 

 the superficial cells are several layers of polygonal cells, while upon 



