168 THE URINARY ORGANS. 



The pelvis of the kidney, centrally situated at one side, is 

 continuous with or forms the upper extremity of the ureter. 



This expanded upper end of the ureter divides into two or 

 three divisions or infundibula, and these into calices into 

 which the apices of the Malpighian pyramids project as 

 papillce. 



The wall of the renal pelvis consists of three layers, mucous 

 (composed of epithelium and a tunica propria), muscular, and 

 fibrous or areolar. The superficial layer of the mucosa con- 

 sists of stratified squamous epithelium, of the variety called 

 transitional, made up of a few layers of cells rapidly changing 

 from the deeper spheroidal to the superficial squamous form. 

 The epithelium rests on a fibrous tunica propria, beneath which 

 is a fibro-muscular layer, containing involuntary muscle-cells. 

 Underneath the latter is a broad layer of fibrous tissue. 

 Within the renal sinus is a variable amount of areolar tissue, 

 extending to the kidney-parenchyma, and usually containing 

 considerable masses of adipose tissue. In this areolar tissue 

 the larger arteries and veins of the kidney are situated and 

 subdivide. The mucosa is said to contain a few small race- 

 mose glands, though the presence of such glands in the urinary 

 tract is disputed. 



The ureter is continuous with the renal pelvis, and its walls 

 consist of three coats, mucous, muscular, and fibrous. 



The mucous coat, which in the contracted ureter is thrown 

 into longitudinal folds, consists of a lining of transitional 

 epithelium, resting on a fibrous layer which represents a 

 tunica propria and submucous layer. The mucosa is said to 

 contain a few small racemose mucous glands. 



Outside the mucosa is the muscular coat, composed of in- 

 voluntary muscle in three layers, an inner longitudinal, a mid- 

 dle circular, and in the lower portion of the ureter a thin 

 outer longitudinal layer. Surrounding the muscular coat is 

 an areolar or fibrous layer. 



The Bladder. 



The walls of the bladder consist of three coats mucous, 

 muscular, and fibrous, from within outward. 



The mucous coat, which is thrown into folds when the organ 



