CTI. VI] 



THE EXCRETORY ORGANS 



aniinals is di\'i«U'tl into a miiiil)C'r of pyramidal portions, the Ijases 

 of which are surrounded liv cortex. Both nieduHa and cortex 

 are largel}' com])osed of uriniferoiis tubules, but the cortex con- 

 tains more blood vessels and is consequently darker in appear- 

 ance. 



The tubules begin as Malpighian capsules and these are 

 confined to the cortex. Each capsule has projecting into it 

 a bunch of coiled capillaries called a glomerulus, and the blood 



Fig. 40. Vertical section of kidney (from Gray), 

 enters these capillaries by a small artery and leaves them b}^ a 

 small vein. 



Each tubule as it leaves its dilated end or Malpighian capsule 

 becomes convoluted, passing through the medulla in the direction 

 of the apex of the pyramid, and then back again to the cortex. 

 The loop which is thereby constituted is known as the loop of. 

 Henle. In the cortex the tubule again becomes convoluted and 

 then after uniting with other tubules ])asses straight to the 

 papilla. The tubules are lined throughout by an epithelium 

 which varies in character in their different parts. The cells 



