33^ THE GENITOURINARY ORGANS. 



tion particularly well seen in sections of the dilated organ. But even 

 here three indistinct muscle layers may be distinguished, the outer 

 and inner layers being longitudinal and the middle circular. A 

 remarkable peculiarity of these structures is the extreme elasticity 

 of their epithelium, the cells flattening or retaining their natural 

 shape according to the amount of fluid in the cavities which they 



aim, rrn 



Fig. 272. Transverse section of the wall of the human bladder, giving a general 

 view of its structure. X I 5- e P> Epithelium ; tp, tunica propria or mucosa ; sm, sub- 

 mucosa ; ilm, inner longitudinal layer of muscle ; rni, circular layer of muscle ; al//i, ex- 

 ternal longitudinal layer of muscle ; ta y tunica adventitia. 



line (compare London, Kann). The terminal blood-vessels of the 

 mucosa of the pelvis of the kidney deserve special mention. The 

 capillaries arise from arterioles which are situated in the ridges of 

 the mucosa above mentioned. The capillaries are peculiar in that 

 they are not completely surrounded by connective tissue, but are 

 in part embedded in the epithelium, the epithelial cells resting on 

 the endothelial wall of the capillaries (Disse). The blood-vessels 

 of the bladder anastomose in the tunica adventitia, smaller branches 

 pass to the muscular tissue. The main stems of the vessels form 

 a plexus in the submucosa, from which arise the capillaries of the 

 mucosa. The veins form submucous, muscular, and subperitoneal 

 plexuses (Fenwick). Lymphatic vessels are found only in the 

 muscular coat and not in the mucosa. 



