230 THE HISTORY OF CREATION. 
still living ostriches, also belong to this group. The Birds 
of the ostrich kind—by giving up the habit of flying, by 
the degeneration of the muscles for flying resulting from this, 
and of the breast bone which serves as their support, and 
by the corresponding stronger development of the hinder 
legs for running—have probably arisen out of a branch of 
the Keel-breasted birds. But possibly, as Huxley thinks, 
they may be the nearest relations of the Dinosauria and of 
the Reptiles akin to them, especially of the Compsognathus ; 
at all events, the common primary form of all Birds must 
be looked for among the extinct Reptiles. 
