654 



THE URINARY ORGANS. 



covered with cylindrical epithelium. The new growth may involve the 

 entire thickness of the wall of the bladder. 



4. A few cases of carcinoma have been described in which the stroma 

 contained a varying quantity of smooth muscle tissue. 



FIG. 416. CARCINOMA OF THE BLADDER. 



Cysts. Dermoid cysts of the wall of the bladder have been described, 

 but are rare. Small cysts with serous contents sometimes occur in the 

 mucous membrane ; a part of them, at least, are believed to be due to 

 faulty embryonal development. 



PARASITES, FOREIGN BODIES, AND CALCULI. 



Among the animal parasites occasionally found in the bladder may 

 be mentioned Echinococcus, Distoma haematobium, Filaria sanguinis, Ascar- 

 ides, and Oxyurides. 



A great variety of foreign bodies may be found in the bladder, par- 

 ticularly in the female. If their stay is long they are apt to become 

 encrusted with urinary salts. 



Calculi. 



Vesical calculi may occur singly or in great numbers, and vary greatly in size, 

 ranging from small, sand-like particles up to masses four or five inches in diameter; but 

 the usual range is from the size of a pea to that of a lien's egg. They are usually oval, 

 spheroidal, or elongated ; or, when several are present, they are apt to be faceted. The 

 surface may be smooth or rough. They are usually more or less distinctly lamellated, 

 and are frequently formed around a central body called a nucleus, which may either be 



