130 Biology in America 



attained fairly respectable dimensions, Pteranodon having a 

 wing spread of twenty to twenty-five feet. This creature 

 with its long arms outstretched, a slender body and narrow 

 neck, at the top of which was poised a long narrow head, about 

 half of which was beak, might well have served as a model 

 for some Egyptian or Assyrian god or goddess. Rhampho- 

 rhynchus, on the other hand, with his long tail, semi-human 

 form and %law-like fingers, would have made a very good 

 model for a winged Satan. 



While the pterodactyls are not directly related to birds, 

 they nevertheless show certain distinctly avian features, one 

 of the most notable of which is the hollow bones. In birds 

 air sacs extend from the lungs throughout the body even into 

 the bones, while the lungs themselves are small, but richly 

 supplied with blood vessels. These air sacs serve as reservoirs 

 for air, somewhat after the manner of a rubber bulb on a 

 pipette, serving to force strong currents in and out of the 

 body through the lungs, and thereby gain efficient aeration for 

 the blood ; which in birds is kept at a high temperature by the 

 active oxidation which takes place in the body in correspond- 

 ence with their great activity. Not only do these spaces in the 

 bones serve as air reservoirs, but they also serve to lighten 

 the bones, increasing their size, relative strength, and surface 

 for attachment for muscles, without unduly increasing their 

 weight; just as the greatest strength in a pillar for a given 

 amount of material is obtained by making the pillar hollow. 



While we know very little about the lungs in the ptero- 

 dactyls it is interesting to find precisely the same adaptation 

 for lightness and strength of bone as we find in the birds. 

 This suggests Lamarck's idea that use (flight) produces 

 change (lightness of bone) in flying reptile as^ in flying bird. 

 But let us not be too hasty in swallowing alluring hypotheses. 

 We find to a certain extent the same air spaces in the bones 

 of the crocodile, which has never had any aspirations for 

 flying, while the lizard, which is also in the main satisfied 

 with a mundane existence, has small air spaces or reservoirs 

 attached to its lungs. Thus we are driven to the conclusion 

 that the pterodactyl and the bird have made use of their 

 opportunities and have learned to fly because they ''were 

 built that way," while the opportunities for flight of the lizard 

 and the crocodile are too small for them to use. 



But there are yet other points of resemblance between bird 

 and pterodactyl. In birds of flight the sternum or breast 

 bone has a prominent ridge or keel like a boat, which has 

 given them the title of Carinatae or keeled. This keel fur- 

 nishes an additional surface for the attachment of the power- 

 ful wing muscles. So too the pterodactyl had a keeled ster- 



