OF ORNITHOLOGY 23 



I MAMMALIA or MAMMALS 



II AVES or BIRDS 



III REPTILIA or REPTILES 



IV BATRACHIA or AMPHIBIANS 

 V PISCES or FISHES 



We have to deal only with the 



GROUP AVES or BIRDS 



The Birds of the World are separated into two great SUB- 

 GROUPS, — according as the Sternum ok Breast-bone 

 is flat or keeled in front. [The extinct species, however, 

 belong to other divisions]. They are, the 



I AVES RATITAE 



(Latin rutin, a raft). Sternum flat. Wings rudimentary 

 and unfit for flight. 



II AVES CARINATAE 



(Latin carina, a keel [of a ship]. Sternum keeled. Pro- 

 vided "with true Wings. 



The first of these divisions embraces the Ostriches, Casso- 

 waries, Emeus, and Birds of a similar nature. 



The second division comprises the majority of known Birds 

 all over the World. 



In treating of the Birds of North America, we have, 

 therefore, to do only with the 



CARINATE BIRDS 



For many years the great assemblage of the Birds of the 

 World have been considered as belonging to three separate 

 spheres of activity : 



1. Those which live in the air, 



2. Those which live upon the ground, 



3. Those which live in the water. 



It has always been so difficult to form any real and stable 

 divisions in this portion of the Animal Kingdom (as in any 

 other portion, in fact) — as one group often so insensibly drifts 



