THE KIDNEY. 183 



and passes directly downward through the medulla, 

 joining other similar tubules dichotomously and 

 becoming larger as it does so, until at length it 

 opens at the apex of a papilla. The uriniferous 

 tubules run an entirely independent course until, as 

 straight tubules, they join one another by twos, to 

 form the outlet ducts. 



We have now to consider the epithelium which 

 lines the tubules. Commencing at the straight 

 tubules in the papillae, we find that in their lower 

 portion they are lined by cylindrical cells with large 

 nuclei and transparent bodies ; further up the cells 

 become more nearly cuboidal, and are often flattened 

 in the medullary rays. The epithelium of the con- 

 voluted and intercalated tubules is similar in charac- 

 ter, and consists of large granular striated cells, 

 whose outlines are not well defined, and which 

 nearly fill the lumen of the tube. The ascending 

 arm of Henle's loop is lined with pyramidal or low 

 cylindrical, granular cells ; while the very narrow 

 descending arm is lined with flat, transparent cells, 

 whose nuclei usually project into the lumen of the 

 tube. 



The glomeruli consist, in the first place, of a mem- 

 branous, apparently structureless capsule, similar to 

 and continuous with the membrana propria of the 

 tubules. The epithelium of the convoluted tubules, 

 as the latter join the glomeruli, becomes flattened 

 and continuous with a layer of very thin transparent 



