BIRD-LIKE EEPTILES. 225 



still living alligators are first met with in a fossil state 

 in the chalk and tertiary strata. The most isolated of 

 the four existing orders of reptiles consists of the re- 

 markable group of Tortoises (Chelonia) ; fossils of these 

 strange animals are first met with in the Jura. In some 

 characteristics they are allied to Amphibia, in others, to 

 Crocodiles, and by certain peculiarities even to Birds, so 

 that their true position in the pedigree of Reptiles is 

 probably far down at the root. The extraordinary re- 

 semblance of their embryos to Birds, manifested even at 

 later stages of the ontogenesis, is exceedingly striking. 



The four extinct orders of Reptiles show among one 

 another, and, with the four existing orders just mentioned, 

 such various and complicated relationships, that in the 

 present state of our knowledge we are obliged to give up 

 the attempt at establishing their pedigree. The most 

 deviating and most curious forms are the Flying Reptiles 

 (Pterosauria) ; flying lizards, in which the extremely elon- 

 gated fifth finger of the hand served to support an enormous 

 flying membrane. They probably flew about, in the 

 secondary period, much in the same way as the bats of the 

 present day. The smallest flying lizards were about the 

 size of a sparrow ; the largest, however, with a breadth of 

 wing of more than sixteen feet, exceeded the largest of our 

 living flying birds in stretch of wing (condor and albatross). 

 Numerous fossil remains of them, of the long-tailed Rham- 

 phorhynchia and of the short-tailed Pterodactylse are found 

 in all the strata of the Jura and Chalk periods, but in these 

 only. 



Not less remarkable and characteristic of the Mesolithic 

 epoch was the group of Dragons (Dinosauria, or Pachypoda). 



VOL. II. Q 



