STRUCTURE OF THE KIDNEY 197 



ment of the Malpighian body furnishes a most favorable 

 opportunity for the passage of substances out of the blood 

 current into the beginning of the tube. 



Uriniferous Tubules. These begin at the glomeruli and 

 end at the apices of the Malpighian pyramids. From their 

 tortuous course in the cortical portion they are there called 

 convoluted tubules, in contradistinction to the straight tubes 

 of the medullary portion. This, however, is only a general di- 

 vision ; further divisions are to be noted. 



The constricted portion of the tube where it leaves the 

 glomerulus is the (i) neck; passing away from the neck the 

 tubule becomes very tortuous and is known as the (2) pri- 

 mary convoluted tubule, which, having run for a variable 

 distance, becomes narrow near the base of the pyramid, and 

 taking a comparatively straight course downward enters the 

 pyramid under the name of the (3) descending limb of 

 Henle's loop ; some of these run nearly as far as the apex, 

 but most of them near the base or middle of the pyramid 

 turn upward forming thus (4) Henle's loop and beginning 

 the (5) ascending limb of Henle's loop; the tube having re- 

 entered the cortical substance becomes convoluted again, 

 (6) secondary convolution, which, by a less tortuous con- 

 tinuation, the (7) intermediate tube, communicates with the 

 collecting tubules, or the (8) straight tubes of Bellini; these 

 last beginning in the cortex, and receiving in their course 

 large numbers of intermediate tubes, enter the base of the 

 pyramid and run in a nearly straight direction toward the 

 apex. About 100 of these straight tubes entering at the base 

 join in their course downward until at the apex they are 

 represented by a single tube. These collections constitute 

 the pyramids of Ferrein ; there are about 12-18 pyramids of 

 Ferrein to each Malpighian pyramid, and as many tubal ori- 

 fices at the apex. The so-called zigzag and spiral tubules 

 are here considered parts of the first and second convoluted 

 tubules. (See Fig. 58.) 



Before they reach the collecting tubules the tubes vary in 



