THE KIDNEY 



181 



widens (50 /A) into a tube the proximal convoluted tubule. This 

 tube (or this portion of the tube) pursues a very tortuous course, 

 always keeping between Ferrein's pyramids, and finally approaches 

 the base of a Malpighian pyramid. Here it assumes an irregular 

 spiral form the spiral tubule (42 /*). 



Afferent arteriole 

 Efferent arteriole 



Spiral 



Descending limb of Henle's \ 

 loop ~~~^( 



Ascending limb 



Henle's loop 



Collecting or straight 

 Principal 



Papillary duct 



FIG. 116. DIAGRAM SHOWING THE DIVISIONS OF A KIDNEY TUBULE. 



The tube suddenly narrows (10 /*), becomes straight, and passes 

 into a pyramid of Malpighi. It reaches sometimes just into the 

 pyramid, more frequently, however, passing deeper than this 

 often descending two -thirds of the distance to the apex; and is 

 called the descending limb of Henle's loop. The descending limb 

 of Henle's loop suddenly turns upon itself, forming the loop of 



