THE EXCRETORY SYSTEM 



221 



single duct in a nearly straight line to the tip of one of the 

 pyramids. There the contents are emptied into the pelvis, 

 whence they immediately 

 enter the ureter. 



Cortex. . 



Malpiqhian 

 Capsule 



Convoluted portion 

 of Tube 



The Renal Blood Ves- 

 sels. The distribution of 

 the blood vessels aids us in 

 understanding how these 

 tubules act. The artery 

 enters the kidney at the 

 pelvis, and breaks up into 

 many small vessels which 

 run toward the surface or 

 cortex of the kidney. Here 

 a minute twig enters each 

 of the little pockets at the 

 beginnings of the tubules 

 (Fig. 110), inside which 

 it breaks up into a roundish 

 knot of capillaries called a 

 glomerulus. After flowing 

 through the capillaries the 

 blood emerges from the 

 pocket as a tiny vein, but 

 does not immediately flow 

 out of the kidney. A part of it enters at once another set of 

 capillaries .that run among the convoluted kidney tubules. 

 After traversing this second set of capillaries, the blood enters 

 definite veins and flows out of the kidney by the renal vein; 

 Fig. 111. 



The Separation of Urea from the Blood. We must 

 keep in mind that the main nitrogenous waste, urea, is 

 made in the liver from materials in the blood and then 

 returned to the blood stream; and that it is only through 

 capillary walls that blood can expel its waste or absorb n3w 



Outlet of 

 Tubule into 

 Pelvis of Kidney 



FIG. 110. DIAGRAM 



Showing the course of two kidney tubules. 

 (Huxley) 



