252 VERTEBRATE ANIMALS. 



birds. Many of the bones, namely, were " pneumatic " that 

 is to say, were hollow and were filled with air, thus giving the 

 animal the degree of lightness necessary for flight. Secondly, 

 while the shoulder-girdle has many of the characters of birds, 

 the breastbone (sternum) is furnished with a prominent ridge 

 or keel, serving for the attachment of the great muscles which 

 work the wings. There can be no doubt, therefore, as to the 

 Pterodactyles having enjoyed the power of genuine flight. 

 Many of them attained no great size, but some of them must 

 have been gigantic, the expanse of wing in one species having 

 been calculated at probably about twenty-seven feet from tip 

 to tip. 



ORDER VIII. ANOMODONTIA (Gr. anomos, irregular ; 

 odous, tooth). This order comprises a few Reptiles which be- 

 long to the Triassic period of geology, and are distinguished 

 by the fact that the jaws were sheathed in horn, so as to form 

 a kind of beak very like that of the Turtles. In some species 

 there appear to have been no teeth at all ; but in one genus 

 there were two long tusks, one on each side of the upper jaw. 

 The limbs were fitted for walking and not for swimming, and 

 these singular Reptiles must, therefore, have been terrestrial 

 in their habits. 



ORDER IX. DEINOSAURIA (Gr. demos, terrible; saura, 

 lizard). In this order are included a number of extinct Rep- 

 tiles, most of which were of gigantic size, and which are con- 

 fined to the Secondary period of geology. They possessed 

 teeth, sunk in distinct sockets, and the limbs were extremely 

 strong, and adapted for progression on land. In some cases 

 the fore-limbs were very much smaller than the hind-limbs, 

 and there is reason to suppose that some of these extraordi- 

 nary animals, though of enormous size, walked habitually 

 upon their hind-legs, like Birds. It is also interesting to note 

 that the gigantic footprints of the Sandstones of the Connecti- 

 cut Valley, formerly regarded as formed by Birds, are now 

 with great probability looked upon as truly the tracks of Dei- 

 nosaurian Reptiles. 



