ie ae 
ee ey 
oie see ht, eee 
CE ein” deans fares ta 0 Se 
ey Nake te ee he he 
en eee fet aE I te ae Set ae eee A eT ae eh 
or Toothed Birds of North America. 267 
Apatornis. These birds were small and wholly unlike Hesper- 
ornis In structure, being, perhaps, as different from that type 
as from that of any modern birds. ey were about the size 
of a pigeon and were provided with very large strong wings, 
but had small legs and feet. The sternum is strongly keeled, 
and the bones are extensively pneumatic. ey present some 
resemblances in structure to the existing Terns, and are thought 
to have somewhat resembled those birds in their mode of life. 
The teeth of Jchthyornis and Apatornis were implanted in 
ia sockets, instead of in a groove, as in Hesperornis. 
An examination of the brain cavity of Zchthyornis presents re- 
sults similar to those arrived at from the comparison of the 
Same part in Hesperornis. If wecompare the skull of Ichthyor- 
ms with that of Sterna—the two being reduced to the same ab- 
Solute size-—we find the brain of the former to have been less 
than one-third the size of the latter. The differences between 
se two smaller birds are the same in kind as those between 
Hesperornis and Ovlymbus (figures 1 and 2), but the cerebral 
hemispheres in Ichthyornis are relatively less elongated than in 
its Cretaceous contemporary. 
_ The similarity in the results of these comparisons is espe- 
cially interesting, since in no other cases have the brain cavi- 
Sion of teeth, is their biconcave vertebra. The presence of 
- reptilian character in vertebrates so highly organized as 
irds, was wholly unexpected, and is only another illustration 
_ OF the fact, so constantly obtruded upon the attention of the 
