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 Fiirbringer 

 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 



