XV CLASSIFICATION 383 
into two sub-classes. One is made up of those which 
have keels to their breastbones, the other of those 
which have a rounded breastbone with no keel. The 
former are called Carinate (carina =a keel); the 
latter, Ratitee (vat7s=a keelless boat). This separates 
off the Apteryx, and the Ostrich with its kin the 
Fic. 75.—Sternum of Ostrich. 
Rhea, the Emeu and the Cassowary. Thus some ten 
species out of the eleven thousand are disposed of. 
I must now mention a few of the points that are 
most useful for deciding to which order one of the 
Carinate belongs. Very important are the following 
questions: the presence or absence of the first toe, 
and the arrangement of the four toes when all are 
