260 WALKS AND TALKS. 



system is intermediate between fishes and reptiles. The ex- 

 tinct Labyrinthodont, while possessing many distinct batra- 

 chiiiu affinities, was reptilian in its crocodile-like skull, and 

 the protective bony plates upon the thorax and flanks. In 

 the teeth is found, however, the peculiar labyrinthine struc- 

 ture seen in some Placoderm fishes; and the sculptured plates 

 of the Ganocephala furnish a resemblance to bony scaled Gan- 

 oids. The structure of Amphibians is on the whole, so rep- 

 tilian that they were, for many years, merged in the reptile- 

 class. Now Amphibians existed, as far as we know, before 

 the reptile-type had been introduced. All their reptilian 

 characters therefore, were prophetic of a class which was yet 

 non-existent. On the contrary, they appeared when the reign 

 of fishes was passing away. All their ichthyic characters, 

 therefore, were retrospective. 



Take next, the wide-ranging class of Reptiles. During the 

 age of its dominance, various ordinal divisions exemplified 

 various relations to the future and the past. While the 

 concavo-convex vertebra was proper to reptiles, the sea-snu ruins 

 had bi-concave vertebrae a reminiscence of fishes. Other 

 reptiles had the teeth soldered to the jaws as in fishes. Some r p- 

 tiles with socketed teeth, however, had bi-concave vertebrae. The 

 Ichthyosaurs, with fish-like vertebra and jaws, had crocodilian 

 teeth and whale-like paddles. It looked forward toward the mam- 

 malian type. Some of the Deinosaurs, also, were prophetic 

 of land-mammals in their short, compact bodies, while their 

 bi-pedal attitude anticipated both mammals and birds. A more 

 explicit anticipation of birds was revealed in the composition 

 of the digits and the structures of the tarsus and pelvis. The 

 Pterosaurs were prophetic of bats in their leathery wings sup- 

 ported by elongated digits. They foreshadowed birds, not alone 

 in the flying function, but in their bird-like scapula, corncoid, 

 and other structures. In one genus the tips of the mandibles 

 were without teeth ; and in the American Pterosaurs, the mandi- 

 bles were completely destitute of teeth, while the tail also, is re- 

 duced to a few vertebra, and the head is distinctly bird-like. 



The gradation of reptiles towards birds brings us to facts 



