242 THE HAUNTS OF LIFE 
that they were adepts, since the breastbone has 
only a slight keel for the fixing on of the 
wing-muscles; and we know that in birds a 
prominent keel is associated with highly de- 
veloped flying power, whereas the running 
birds like the ostrich have no keel at all. 
On the other hand, the Flying Dragons 
show, as flying birds do, a solidifying of the 
middle part of the backbone, giving the 
wings a firm fulcrum against which to work. 
It is probably quite safe to say that the 
Pterodactyls represent a “lost race”; they 
certainly were not the ancestors of birds. It 
may be, however, that the ancestors of the 
Pterodactyls and the ancestors of our birds 
were related to one another. 
THE FLIGHT OF BIRDS 
The third solution was a triumphant one: it 
gave birds their mastery of the air. ‘There 
seems no doubt that birds sprang from an 
extinct stock of Dinosaur reptiles which had 
become bipeds; and it is highly probable that 
they were to begin with swift runners that 
flapped their scaly fore-limbs and took long, 
skimming leaps along the ground. When 
