Mammalia. 115 



UEINAEY OEGANS General. 



The Mammalian Kidney is distiny,uislied from tliat of all 

 otlier Yertebrata by tbe bipartite division of its substance 

 into a * cortical ' and a ' medullary ' portion. The Cortical f 

 secretory portion, is highly vascular, and composed mainly of 

 tortuous tubes, which, taking their origin from the Malpighian 

 bodies, converge towards the interior and do not spread to the 

 exterior of the gland. The Medallari/y excretory portion, is 

 composed mainly of straight tubes converging to meet at the 

 apex of the medullary pyramid : it contains no Malpighian 

 bodies. The secreting tubuli generally terminate by one 

 or more papilla) in a dilatation at the commencement of the 

 ureter called the pelvis. In many Mammals the right kidney 

 is placed higher than the left ; the reverse of that commonly 

 observed in the Human subject. The Eenal artery alone, 

 derived directly from the aorta, supplies both the substance of 

 the kidney and the secreting organism : in discharging the 

 latter function, the afferent vessels form vascular tufts in the 

 Malpighian bodies, and the efferent vessels proceeding thence 

 form capillary plexuses surrounding the uriniferous tubes. 

 The Capillaries after they reunite to form venules round the 

 papillae sometimes assume a starlike, or an arborescent dispo- 

 sition, or even form a network on the surface of the kidney 

 prior to dipping down through the cortical septum to emerge 

 at the hilus. In all cases the ultimate venous trunks teim- 

 inate in the vena cava inferior and their component veins 

 never anastomose ivith the Intestinal veins. In the Human 

 Embryo the Kidneys consist of several masses or lobes, as it 



