RENAL SECRETION. 



641 



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 arter}', the vas afferens, 

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

 as to be surrounded by a double laj^er of the bladder-like expansion of 



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

 Tysox and Hexle. {Lumluix.) 



1, cortex; If, medullary rays; UMabyrinth; 2, medulla ; 21. papillary portion of the medulla; VI 

 boundary layer of the medulla? 3, transverse action of tubules in boundary layer ; 4 fat of renal s nue ; 

 5, artery ; *, transversely eoursing 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 



41 



