FLYING DRAGONS. 39 



statement that an immature skull of one of the species measures upwards of G feet, 



while fully adult ones must have been considerably larger. The extraordinarily 



small size of the brain of these creatures is indicated in the lower figure of 



the skull. Externally the bodies of these dinosaurs were protected by granules 



and plates of bones, which, 



like those of crocodiles, were 



probably overlain with horny 



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 pd, chin-bone. Other letters as in the figure on p. 4.— After Marsh. 



causing the whole pelvis to 



simulate that of the carnivorous group, to which it has no real resemblance. 



We have yet to learn the reason why, at the close of the Secondary period, 

 these mighty dinosaurs, together with the flying dragons 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 

 unknown and the latter but poorly represented, the place of both was taken by 

 the flying 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 breast-bone and 

 general form of the collar-bones (although these are not welded together into a 

 furcula), the pterodactyles 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 atten- 

 tion as existing between totally different groups of animals whose mode of lite 

 is similar. 



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

 modifications 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 con- 



