194 



EXCRETION BY THE KIDNEYS AND SKIN 



the upper, one toward the lower and one toward the central 

 portion of the organ. These are the three infundibula. Each 

 infundibulum, passing outward, subdivides into two or three, or 

 more, short cylinder-like canals which receive the apices of the 



Boundary or 

 I ^marginal 

 zone. 



FIG. 55. 



LS, of a pyramid of Malpighi; PF, pyramids of Ferrein; RA, branch of renal 

 artery with an interlobular artery; RV, lumen of a renal vein receiving an inter- 

 lobular vein; VR, vasa recta; PA, apex of a renal papilla; b, b, embrace the bases of 

 the lobules. (Stirling.) 



pyramids. These are the calyces, each of which receives the 

 apex of one or more pyramids. The urine thus escaping from 

 the pyramidal tubules passes in succession through the calyces, 

 infundibula, pelvis, and thence into the ureter. 



The cortical substance constitutes the outer layer of the kid 



