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 Carinatae {carina — a keel] ; the 

 latter, Ratitae 'vat is = a keelless boat). This separates 

 off the Apteryx, and the Ostrich with its kin the 



Fig. 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 arc 

 most useful for deciding to which order one of the 

 C annate 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 



