THE KIDNEYS. 



minute conical masses of renal substance, the cortical lobules, the bases of which lie 

 at the surface and the apices within the pyramids of the medulla. From the fore- 

 going it is evident that each renal pyramid corresponds to a group of cortical lobules, 

 the tubules of which, on entering the medulla, become progressively less numerous 

 but larger, in. consequence of repeated juncture, until, as the wide excretory ducts, 

 they end at the summit of the papilla. The relations of the pyramids to the papillae 

 are less simple than formerly recognized, since, instead of each of the latter embracing 

 but one of the former, Maresch * has shown that a single papilla, as a rule, includes 

 from two to four pyramids, 

 which are blended into one FIG. 1 599. 



COnical maSS Culminating in Labyrinth Med. ray Labyrinth 



the papillary apex. 



Structure of the Kid- 

 ney. The fundamental 

 components of the verte- 

 brate excretory organ, both 

 in the fcetal and mature con- 

 dition, include ( i ) a tuft of 

 arterial vessels derived more 

 or less directly from the 

 aorta, (2) tubules lined with 

 secretory epithelium, and 

 (3) a duct for the convey- 

 ance of the excretory pro- 

 ducts. These constituents 

 are represented in the kid- 

 ney of man and the higher 

 animals by ( i ) the glomeru- 

 lus, (2) the convoluted uri- 

 niferous tubules, and (3) the 

 collecting tubes, pelvis, and 

 ureter. Since, in a general 

 way, to the epithelium lining 

 the tubules may be ascribed 

 the function of taking from 

 the circulation the more solid 

 constituents of the urine, 

 and to the glomerulus the 

 secretion of its watery parts, 

 obviously the most favora- 

 ble arrangement to secure 

 the removal of the excretory 

 products is one insuring 

 flushing of the entire tubule 

 with the fluid secreted by 

 the glomerulus. Such ar- 

 rangement implies the loca- 

 tion of the vascular tuft at the very beginning of the tubule, a disposition which 

 in fact is found in the kidneys of all higher animals. The number of the glomeruli, 

 therefore, corresponds with that of the uriniferous tubules, each of which begins in 

 close relation with the vascular tuft. The kidney-substance consists of an intricate 

 but definitely arranged complex of uriniferous tubules, supported by the interstitial 

 connective-tissue stroma, which have their commencement in the cortex and their 

 termination at the apices of the papillae, their intervening course being marked by 

 many and conspicuous variations in the character, size, and direction of the tubules. 



The uriniferous tubule begins as a greatly expanded blind extremity, the 

 capsule (i), which surrounds the vascular tuft or gloutcntlns, the two together con- 

 stituting the Malpighian body, which lies within the labyrinth. On leaving the Mal- 



'Anatom. Anzeiger, Bd. xii., 1896. 



Proximal con- 

 voluted tubule 



Intermediate 



tubule I distal 

 convoluted) 



Intermediate 



tubule 



Efferent vessel 

 Neck 



Afferent vessel 

 Capsule 

 Interlobular 



artery 



Descending 

 limb 



\scendiii 



limb 



iup of Henle 



Papillary duct 



Papilla 

 Diagram showing course of uriniferous tubule. 



