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THE URINARY SYSTEM 



The following tabular resume may be of service by emphasizing 

 the more important peculiarities of the several portions of the uri- 

 niferous tubule. 



BLOOD SUPPLY. The kidney receives its blood supply from 

 the renal artery, which, as it enters the hilum, divides into two sets 

 of principal branches, of which the ventral set supply one-fourth, 

 the dorsal set three-fourths of the renal substance. These princi- 

 pal branches, the arterice proprice renales, are embedded in the 

 connective tissue of the hilum and follow the walls of the infundi- 

 bula and calyces, upon which they lie, thus reaching the columns 

 of Bertini between the renal calyces. Here they enter the cortical 

 substance and divide, each branch passing in a curved or arched 

 manner beneath the base of the adjacent Malpighian pyramids. 

 These vessels form an incomplete arterial arcade which lies in the 

 margin of the cortex at the outer border of the medullary bound- 

 ary zone. 



From the arterial arcade, branches are given to the medullary 

 tissue of the Malpighian pyramids on the one hand, and on the 

 other to the cortical substance. Those branches which enter the 

 medulla are slender vessels which pursue a characteristically 

 straight course between the parallel tubules of this region and are 



