DEFINITION OF BIRDS 



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two other primary divisions of the class, Odontotormm and Odontolcce, 

 or Birds with teeth in sockets, and those with teeth in grooves. In 

 both these genera the tail is short, as in ordinary birds. In Iclithy- 

 m-iiis, though the wings are well developed, with fused metacarpals, 



Fig. 15. — Restoration of Hesperornis regalis. After Marsh. 



and the sternum is keeled, the vertebrae present the extraordinary 

 primitive character of being biconcave. In Hesperornis the vertebrae 

 are saddle-shaped, as usual, but the sternum is flat, as in the existing 

 ostriches, and the wings are rudimentary, wanting metacarpals. 

 Some twenty species of several genera of other American Cretaceous 



H 



