2396 CROCODILES, DINOSAURS, AND FLYING DRAGONS 



shields. It has yet to be mentioned that in the horned dinosaurs, as shown in the 

 figure of the skeleton, the posterior bar of the pubis has disappeared, and only the 



front branch remains, thus 

 causing the whole pelvis to- 

 simulate that of the carnivor- 

 ous group, to which it has no 

 real resemblance. 



We have yet to learn the 

 reason why, at the close of 

 the Secondary period, these 

 RESTORATION OF THE SKELETON OF A HORNED DINOSAUR, mighty dinosaurs, together 



pd. chin bone. Other letters as in the figure on p. 2360. After Marsh, with the flying dragOHS which 



at the same time tenanted the 



air, and the fish lizards and plesiosaurs which peopled the sea, should, one and all, 

 disappear and that apparently suddenly to make way for mammals and birds, 

 which henceforth became the lords of creation. 



FLYING DRAGONS, OR PTERODACTYLES 

 Order ORNITHOSAURIA 



At the present day bats and birds are the only Vertebrates endued with the 

 power of true flight, but during the Secondary period, when the former were un- 

 known and the latter but poorly represented, the place of both was taken by the fly- 

 ing dragons, or, as they are called, from the structure of their wings, Pterodactyles. 

 While agreeing with crocodiles in the essential structure of their skulls and in their 

 two-headed ribs, these curious reptiles have the other portions of their skeleton 

 more or less specially modified for the purposes of flight. In the relatively-large 

 size of the brain which is doubtless essential for a flying animal and general 

 bird-like form of the skull, as well as in the keeled breastbone and general form of 

 the collar bones (although these are not welded together into a furcula), the ptero- 

 dactyles present a curious similarity to birds. Misled by these resemblances, some 

 anatomists have, indeed, been induced to consider that the two groups are nearly 

 related, although a more mistaken notion never existed. Such resemblances as do 

 exist between the two groups are due, indeed, to that parallelism in development to 

 which we have already had occasion to call attention as exisiting between totally 

 different groups of animals whose mode of life is similar. 



The most distinctive feature of the pterodactyles is to be found in the modifica- 

 tions of the bones of the fore-limbs for the purpose of supporting a wing, which 

 took the form of a membranous expansion of skin analogous to that constituting 

 the wings of bats. This wing was mainly supported by the great elongation of the 

 bones of the fifth digit or finger of the fore-limb, as shown in the figure of the skel- 

 eton on the following page, and likewise in the restored representation of one of these 

 reptiles. The membrane thus supported seems to have extended backward along 



