170 



ANIMAL PHYSIOLOGY. 



distinct renules, completely separable one from another, and 

 every one possessed of a cortical covering and a medullary 

 part gathered into a cone like that of a rabbit's kidney. In 

 the seal these renules are distinct, but cannot be dissected 

 separate; while in the ox they are fused more closely together, 

 but form separate lobules on the surface. 



The human kidney has the smooth surface of that of the 

 sheep, but in construction more nearly approaches to that of 

 the ox. Before birth, it presents a lobulated appearance 

 of the surface (fig. 85) like the ox kidney; but the lobules 

 become so fused together that their outlines are soon oblite- 

 rated, and the general surface made smooth like the kidney 

 of the sheep. The construction, however, is at once manifest 

 on laying the organ open by a vertical section from the hilus 

 to the outer border. Then it is seen that the medullary 

 substance consists of a number of cones distinct each from 

 the rest, being separated by extensions of the cortical part. 



Fig. 90. KIDNEY OF SEAL, ver- 

 tical section. 



Fig. 91. HUMAN KIDNEY, ver- 

 tical section." 



These are called pyramids of Malpiglii ; and while their 

 bases are imbedded in the cortex, the apex of each projects 

 into a cup or calyx which embraces it; and the calyces 

 open, each by a constricted orifice opposite the apex of the 

 pyramid which it embraces, into the pelvis of the kidney, 



