THE URINARY ORGANS. 



261 



the renal sinus where they form papillae. The 

 medullary substance is more dense than the cortical 

 and is strictly striated, which is due to the radiating 

 course of the tubules in this part. At the base of 

 each Malpighian pyramid these tubules pass up into 

 the cortical substance and are grouped to form 

 cone-like masses called medullary rays, or pyramids of 



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Capsule. 



Glomeruli. 



Pyramid of Ferrein. 



Malpighian 

 pyramid. 



Fig. 199. Section through cortex and medulla of kidney. 



Ferrein, the apex of each being in close proximity to 

 the periphery of the kidney. There are thus a great 

 many medullary rays for each Malpighian pyra- 

 mid. The portions of the kidney that intervene 

 between the medullary rays are called the labyrinth, 

 and consist largely of convoluted tubules. The 

 cortical substance not only covers the bases of the 



