EEXAL SECRETION. 



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in the medullary portion of the kidney, 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 afferens, 

 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 



FIG. 265. NAKED-EYE APPEARANCES OP THE KIDNEY OF MAN, AFTER 

 TYSON AND HENLE. (Landois.) 



1, cortex; If, medullary rays; 1", labyrinth; 2, medulla; 2f, papillary portion of the medulla; 2'f, 

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

 5, 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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