URINAliY SYSTEM OF BIRDS. 227 



to the risings and depressions of the pelvis ; the anterior surface is 

 smoothly convex or flattened ; but rising into a series of promi- 

 nences which correspond, not to the eminences, but to the cavities 

 of the bones on which they rest ; their inner or mesial side is 

 generally pretty regular and straight, but the external edge is 

 more or less notched. They are relatively larger than in most 

 Mammals ; resembling in this respect the kidneys of Whales and 

 of the cold-blooded Ovipara, Avhere there is no perspiration from 

 the skin. 



The kidneys vary in size in different birds, being, for example, 

 smaller in most of the Grallatores^ as the Bustard and Heron, 

 where the pehds is short, than in the Rasorial Order, in which it 

 is of great extent. Where they are short they are in general 

 more prominent, and this is so remarkable in some Birds, as the 

 Owls, that in them they resemble somewhat in their superficial 

 position the kidneys of Mammals. 



As might be expected from their relations to the pelvis, the 

 kidneys in Birds present as many varieties of outward configuration 

 as there are differences in the part of the skeleton to which they 

 are moulded. In some Aquatic Birds, as the Grebe (Podiceps) and 

 the Coot [FuUca), the kidneys are more or less blended together 

 at their lower extremities, as in most Fishes : in Colymhus the 

 extent of the union is greater ; in Platalea they have been observed 

 to be joined by a middle band. In the rest of the class they are 

 distinct from one another. 



The principal lobes are in general three in number : the anterior 

 or highest one is, in some cases, the largest; while in others, 

 as the Pelican, the contrary obtains, the lowest division being 

 most developed in this bird. In the Tern each kidney is divided 

 by fissures into seven or eight square-shaped lobes : in the Eagle 

 they each present four divisions ; but in these cases there are not 

 distinct ureters to each lobe as in the subdivided kidneys of 

 Mammals. In the Emeu {Dromaius ater) the kidney presents only 

 two lobes ; the superior or anterior one is the broadest and most 

 prominent, being of a rounded figure, and constituting one-third of 

 the whole ; the lower division is flattened, and gradually tapers to 

 a point. In one specimen I found the left kidney half an inch 

 longer than the right. In tlie small Cantores the exposed super- 

 ficies of the kidney is rarely lobular. 



Each kidney is invested by its proper capsule, a thin membrane, 

 which also extends into the substance of the gland, between its 

 divisions: a layer of peritoneum is reflected over their anterior 

 surfaces. 



Q 2 



