VERTEBRATA 163 



from Madagascar (sEpyornis) and from New Zealand, 

 the moa (Dinornis). This singular geographical distri- 

 bution, like that of the Dipnoi and marsupials, shows 

 that the group was once widely spread over the earth, 

 but is now greatly restricted in area. 



DIVISION B. Carinatae 



Birds which, with rare exceptions, e.g., the Penguins, 

 have a keeled sternum, and developed functional wings. 



Of the birds composing this division, some live mainly 

 in the water, others on the land, while still others spend 

 a considerable- part of their lives on the wing. Their 

 bodily structure is, consequently, modified to suit their 

 mode of life. Hence, they may be broadly grouped 

 into aquatic, terrestrial, and aerial birds. 



A. AQUATIC BIRDS. Specially organized for swim- 

 ming ; the body flattened, and covered with water-proof 

 clothing feathers and down ; the legs short (the knees 

 being wholly withdrawn within the skin of the body), 

 and set far apart and far back ; the feet webbed, and 

 hind toe elevated or absent. The legs are always feath- 

 ered to the heel at least. They are the only birds whose 

 neck is sometimes longer than the legs. 



Examples, penguins, ducks, petrels, and gulls. 



B. TERRESTRIAL BIRDS. This group exhibits great 

 diversity of structure ; but all agree in being especially 

 terrestrial in habit, spending most of the time on the 

 ground, not on trees or the water, although many of 

 them fly and swim well. The legs are long or strong, 

 and the knee is free from the body. The hind toe, when 

 present, is small and elevated. Such birds are the storks, 

 plovers, and turkeys. 



C. AERIAL BIRDS. This highest and largest group 

 includes all those birds whose toes are fitted for grasping 

 or perching, the hind toe being on a level with the rest. 



