OF ornith()L()(;y 23 



I MAMMALIA or MAMMALS 



II AVES or BIRDS 



III REPTILIA or REPTILES 



IV BATRACHIA or AMPHIBIANS 

 V PISCES or FISHES 



We liavo to deal only with tlic 



GROUP AVES or BIRDS 



The Birds oi' the World are separated into two great tSUB- 

 GKOUPy, — aeeordiug as the Sternum oe Breast-bone 

 is FLAT or KEELED iu front. [The extinct species, however, 

 belong to other divisions]. They are, the 



I AVES RATITAE 



(Latin /(fZ/.s, a ratt). Sternnni flat. Wings rudimentary 

 iind unfit for Hight. 



II AVES CARINATAE 



(Latin rarbm, a keel [of a ship]. iSternuni 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 

 idl 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 : 



L Those which live in the air, 



2. Those which live upon the ground, 



3. Those which live in the water. 



It has alwavs been s(» 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 



