THE PRINCIPAL BIRD GROUPS 55 



Much difference of opinion exists not only 

 respecting the taxonomic value of various 

 anatomical characters, but as regards the affini- 

 ties and relationships of these groups, as well 

 as the position in the avine system of not a 

 few aberrant forms. But on the other hand 

 opinion is much less divided, if not in com- 

 plete accord, amongst systematists respecting 

 the composition of the several great groups 

 which we will shortly proceed to describe at 

 some length. Birds naturally separate them- 

 selves, as we have already seen, into two great 

 primary divisions — one the Carinatae, possessing 

 a keel to the sternum, the other Ratitae, in which 

 this keel is absent. This latter division is com- 

 posed entirely of birds in which the faculty of 

 flight is wanting ; and as Professor Furbringer 

 seems to have demonstrated, these birds are 

 the retrograde or degenerate descendants of 

 birds that possessed volant powers — the body 

 increasing in bulk as the muscular power of the 

 wings decreased. There can be no doubt that 

 the Ratitae comprise the most archaic of exist- 

 ing birds, so that we may appropriately com- 

 mence our survey of the principal avine groups 

 with a brief notice of them. Huxley divided the 

 Ratitae into five distinct groups, one of which 



