OEGA.NIZATION OF THE OENITHOSAUEIV. 87 



identity of structure is due to identical causation, unless we have 

 at least some evidence to the contrary. If the formula adaptive 

 modification means that the Pterodactyles acquired by flight lungs 

 similar to those of birds, it seems as though it were only an- 

 other and less striking way of saying that reptiles are birds. If 

 Professor Huxley could give to reptiles a bird-like heart and bird- 

 like lungs, it would be important to learn the characters by which 

 they could still be recognized as members of the class Eeptilia. 



The only remaining vital character which can be recognized 

 in a fossil is the brain ; and if the respiratory system of a rep- 

 tile could become adapted so as to be undistinguishable from that 

 of a bird, what reason is there that it should not be supposed 

 that the brain also of a flying reptile would become indistinguish- 

 able from that of a bird ? 



But between birds and Ornithosaurs there is a great struc- 

 tural resemblance in the brain. A bird's brain so fills its brain- 

 case that a mould of this chamber gives a true idea of the form of 

 the brain. The evidence for the identity of cerebral structure 

 in these two groups rests upon the form of the cerebral hemi- 

 spheres in the Pterodactylus longirostris and on other specimens 

 from the lithographic slate, on an undescribed skeleton from the 

 Wealden of the Isle of "Wight, preserved in the collection of 

 the Eev. "W. Darwin Fox, and on several fragments showing dif- 

 ferent portions of the brain-cavity of the OrnithocJieirus in the 

 Cambridge Upper Grreensand. That these latter fossils do not 

 pertain to true birds, remains of which also occur in the deposit, 

 but really belong to Ornithosaurs, is demonstrated by the associ- 

 ation of the similar Wealden cranium with a typical Pterodactyle 

 skeleton. 



The Upper- Greensand specimens on which I rely for evidence 

 as to cerebral characters are two in number — first, the hinder 

 part of a cranium, and, secondly, a mould of the upper por- 

 tion of the brain-cavity. The former specimen is in the Wood- 

 wardian Museum of the University of Cambridge, and the latter in 

 that of J. P. Walker, Esq., M.A., P.L.S. The Woodwardian spe- 

 cimen shows a vertical section of the brain made in about the line 

 of junction of the frontal with the parietal bones, or just behind that 

 line (PI. XI. fig. 4). I have excavated the brain-cavity a little, so 

 as to make its outlines distinct ; but the hard and brittle character 

 of the specimen rendered it impossible to remove the material 

 which fills it. In its greatest lateral width it measures -ff of an 



