EENAL SECEETION. 



641 



in the medullary portion of the kidne}', form, by frequent subdivisions, 

 a series of straight, branching canals, the so-called urinary tubules. 

 After frequent subdivision each branch terminates in a looped tubule, 

 which after undergoing various convolutions in the cortical portion of 

 the kidney, terminates in a bladder-like expansion. In each of these 

 expansions enters a small branch of the renal artery, the vas afferent, 

 which undergoes division into a bunch of capillaries which is so placed 

 as to be surrounded by a double layer of the bladder-like expansion of 



Pig. 265.— Naked-Eye Appearances of the Kidney of Man, after 

 Tyson and Henle. (Landois.) 



1, cortex; V, medullary rays; l'Uabyrinth; 2, medulla ; 2', papillary portion of the medulla ; 2", 

 boundary layer of the medulla : 3, transverse section of tubules in boundary layer ; 4, fat of renal sinus , 

 6, artery; *, transversely coursing medullary rays; A, branch of renal artery; C, renal calyx; U, ureter. 



the tubules. The relation between this bunch of vessels and the expan- 

 sion of the tubules is similar to what would be expected if a tip of the 

 finger of a glove was inverted from the outside. The collection of capil- 

 laries is, therefore, in contact with the external layer of the tubule, and 

 is surrounded by a space which is in direct communication with the in- 

 terior of these tubes. After having undergone subdivision into capilla- 

 ries in this expansion of the tubules, the efferent vessel, which collects 



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