FOUND LINKS. 125 



the jaws. In so far as Hesperornis is concerned, it 

 removes the bird-class, on the face o things, a step 

 nearer to the reptile hosts. Formerly, part of the 

 naturalist's definition of a bird was included in the 

 declaration that teeth were wanting. Now, the defi- 

 nition requires stretching, to include a character 

 which is shared in by certain reptiles, just as others, 

 represented by tortoises and turtles, imitate the tooth- 

 less condition of existing birds. 



But the Ichthyornis of the Chalk is even a more 

 remarkable bird-fossil than' Hesperornis. For the 

 teeth of the former are implanted in distinct sockets, 

 whilst its breastbone had a keel, and its wings are of 

 large size, and indicate the possession of bird-habits, 

 united to structures of reptilian kind. But more 

 peculiar still, as a departure from bird- characters was 

 the nature of its vertebrae or the joints of the spine ; 

 for Ichthyornis possessed vertebras, which, like those 

 of the fishes and of extinct reptiles, were hollow at 

 either end. Such a feature must naturally be made 

 much of in estimating the relationship of this old 

 bird to the reptilian hosts. The size of Ichthyornis 

 was that of a pigeon. 



Preceding these birds in time comes the ArcJice- 

 opteryx of the Upper Oolite deposits of Solenhofen, in 

 Bavaria. Here the reptile-characters increase in 

 number as becomes the older nature of their possessor. 

 A recently -procured specimen of this bird enabled a 

 zoological authority to declare that it was certainly 

 not wholly a bird, and as certainly not wholly reptile 



