124 NATURE STUDIES. 



to the exertions of Professor Marsh, appear before 

 us as veritable links, connecting the birds and 

 reptiles in respect of their teeth, as well as in other 

 features of their economy. Hesperornis stood at least 

 five feet high, and in respect of its bony framework 

 exhibits a close alliance with the grebes of our own 

 day. But, strange to say, Hesperornis wants one 

 marked peculiarity of other birds (save the ostrich 

 group), namely, the prominent " keel" or bony ridge 

 on the breast-bone, to which the wing-muscles of 

 birds are attached. The wings were certainly of 

 rudimentary character, but this is a feature we see 

 exemplified in the auks and penguins of our own day; 

 and it is probable that the tail of this great diver of 

 the chalk seas was unusually mobile, and adapted 

 possibly to serve as a rudder. The reptile characters 

 crop out, however, most clearly in the teeth of this 

 bird. There were no teeth in the front of the upper 

 jaw, and presumably this region was covered with a 

 horny beak. The teeth themselves are curved struc- 

 tures ; but they are set in a common groove, and not 

 lodged each in a socket, as is commonly the case in 

 higher animals. In living reptiles themselves, it may 

 be added, the teeth, save in crocodiles, are not 

 implanted in sockets. Thus, in serpents and lizards 

 the teeth are simply united by bony union to the 

 bones which bear them; but certain extinct lizards- 

 had socket-fastened teeth, and the giant fossil reptiles 

 (Ichthyosaurus, &c.) of the Lias, Oolite, and Chalk, 

 possessed teeth which likewise arose from sockets in 



