428 prof. r. owen on the modifying influence 



Discussion. 



Professor Seeley gathered that the chief object of Prof. Owen's 

 paper was to show that the modern Crocodiles have been evolved 

 from those of the Secondary rocks, and in consequence of the 

 altered conditions of their struggle for existence which resulted from 

 the development of mammalian life in Tertiary as compared with 

 earlier ages. While admitting the evolution, he thought it had no 

 necessary dependence upon the incoming of mammalian prey. Thus 

 the removal backward of the palato-nares in the modern Crocodiles 

 was a condition that would be gradually and inevitably developed, 

 even if mammals had not existed. In the living Crocodile these 

 nares are surrounded by the pterygoid bones, and to the dorsal 

 surface of those bones enormous muscles are attached, which form 

 great hemispherical masses on each side of the head, and are 

 attached to the inner side of the lower jaw. But in the Secondary 

 Crocodiles this pterygoid region of the palate makes a nearer 

 approach to the condition of the bones and palato-nares in certain 

 lizards. And since in the lizards the internal pterygoid muscle has 

 no such development, owing to the larger size of the temporal 

 muscle, he considered that the gradual increase in size of the 

 pterygoid muscles, consequent on the lateral action of the jaws in 

 tearing food, was the cause of the osseous differences of the palate 

 in this region in the two types, because the tension of the muscles 

 acting on the pterygoid bones at their suture with the palatines 

 would cause those bones to elongate, and as the muscles grew more 

 powerful the palato-nares would thus be carried further and further 

 backward with the bones which embrace them ; and similarly, by 

 lateral tension, the pterygoid bones would grow in the line of the 

 median suture and so widen, while they reduced the size of the 

 aperture of the palato-nares. This physiological explanation seemed 

 to be independent of the condition of prey being mammalian. 



Dr. Meryon was sorry that the author had not gone to the full 

 length in regard to evolution, and, referring to the backward posi- 

 tion of the palato-nares, said that this was a provision adapted to 

 their holding their prey under water to drown it. He also referred 

 at some length to the influence of the nervous system in inducing 

 changes. 



Mr. Htjlke observed that with respect to Prof. Owen's idea that « 

 warm-blooded animals were not preyed on by the Mesosuchian 

 Crocodiles, it could not be doubted that such did actually exist 

 contemporaneously with them, and that they might become an easy 

 prey when fording rivers or lakes, as at the present time. He 

 thought that the inference drawn from the strong scutal armour of 

 the Mesosuchia, that these lived in presence of stronger and larger 

 animals, and so stronger armour was necessary for their defence, was 

 not justified by the facts of to-day. The Jacquari of Tropical America, 

 as an example, is similarly armoured, yet has no larger and stronger 

 adversaries. In referring to the suggestion that the backward posi- 

 tion of the palato-nares was an adaptation to exclude the entrance of 



