EXCRETION. 



425 



*n 



tt 



acute angles a number of branches (Fig. 193). 



base of the pyramids they are known as the tubules of Bellini. In 



the cortical portion of the kidney the tubule becomes enlarged and 



twisted, and, after pursuing an extremely convoluted course, turns 



backward into the 



medullary portion for i" 



some distance, form- 



ing the ascending limb 



of Henle's loop; it 



then turns upon itself, 



forming the descend- 



ing limb of the loop, re- 



enters the cortex, again 



expands and becomes 



convoluted, and finally 



terminates in an ovoid 



enlargement known as 



Miiller's or Bowman's 



capsule, in which is 



contained a small tuft 



of blood-vessels the 



glomerulus._ Each 



turjule consists of a 



basement membrane 



lined throughout its 



entire extent by epi- 



thelial cells. The epi- 



thelium as well as the 



tubule vary in shape 



and size in different 



parts of its course. Jn, 



the capsule the epi- 



thelium is flattened, 



lining not only the 



inner surface of the 



capsule but reflected 



over the ^lood- vessels 



as well! This is 



known as^he glomer- 



ular epithelhuji._ In_ 



the convoluted por- 



tions of the tubules the epithelium is cuboidal, granular, and some- 



what striated; in Henle's loop it is more or less flattened. 



The Blood-vessels of the Kidney. The renal artery enters the 

 kidney at the hilum behind the ureter; it soon divides into several 



FIG. 192. LONGITUDINAL SECTION THROUGH THE 

 KIDNEY, THE PELVIS or THE KIDNEY, AND A 

 NUMBER OF RENAL CALYCES. A. Branch of the 

 renal artery. U. Ureter. C. Renal calyx, i. 

 Cortex, i'. Medullary rays. i". Labyrinth, or 

 cortex proper. 2. Medulla. 2'. Papillary por- 

 tion of medulla, or medulla proper. 2". Border 

 layer of the medulla. 3, 3. Transverse section 

 through the axes of the tubules of the border layer. 

 4. Fat of the renal sinus. 5, 5. Arterial branches. 

 *. Transversely coursing medulla rays. (Tyson, 

 after Henle.) 



