Page:The Fauna of British India, including Ceylon and Burma (Birds Vol 1).djvu/40

8 presence or absence of a median keel to the sternum. But these groups, though accepted by Blanford and Oates, are very unsatisfactory, since in some flightless Carinatæ the sternum has become reduced to the Ratite condition.

Taking into consideration birds both living and extinct, we have two well-defined sub-classes, the Archæornithes and Neornithes.

The first is reserved for the Archæopteryx with an elongated reptilian chain of caudal vertebræ, each bearing a pair of rectrices and having the jaws armed with teeth. The sub-class Neornithes