FLIGHT OF ANIMALS — GRAY 



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drive the animal along in the air comes from gravity in a way which 

 we shall consider later. 



Among living reptiles, only one rather doubtful glider is known — 

 the so-called flying dragon {Draco volens). This odd lizard has a 

 flexible membrane down each side of its body, and it is said to glide, 

 like the flying frog, by jumping off trees. It seems strange that there 

 are no other living flying reptiles, when one remembers the great 

 pterodactyls of prehistoric times. Pterodactyls (meaning wing-fin- 

 gers) had enormously enlarged fourth fijigers from which membranes 

 spread across to the body and hind legs : their wings sometimes had 

 a span of 20 feet (fig. 2). If you want to imagine what they looked 



Figure 2. — The pterodactyl, showing the enormously enlarged fourth fingers, with mem- 

 branes extending to the body and hindlcgs to form wings. 



like you camiot do better than read Conan Doyle's *'Lost "World." Un- 

 like birds, pterodactyls had poorly developed breast muscles; active 

 flapping flight must have been impossible ; how these gliding monsters 

 launched themselves, either from trees or from the tops of steep cliffs, 

 we do not know. 



And now we come to the greatest of all flying animals, the birds. 

 The mastery of birds over air is incomparably greater than that of 

 any other group of animals, and we shall have to examine them in 



