8 



AYES. 



presence or absence of a median keel to the sternum. But these 

 groups, though accepted by Blarit'ord and Gates, are very un- 

 satisfactory, since in some flightless Carinatce 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 ArchceornitJies and NeornitJies. 



rnxjp 



Under view of tb skull of a Raven, vo, vomer; mxp, maxillo-palatine 

 process ; pa, palatine ; ptg, pterygoid ; q, quadrate ; b.sph, basi-spbenoid ; 

 sph.r, sphenoidal rostrum. 



The first is reserved for the Arclueopteryx with an elongated 

 reptilian chain of caudal vertebrae, each bearing a pair of rectrices 

 and having the jaws armed with teeth. The sub-class Keornithes 



