OP A HIGHER FORM OF LIFE ON A LOWER FORM. 



423 



connected with the disappearance of Eeptilia, against the attacks of 

 which a better coat of mail may have advantaged the contemporary 

 Mesozoic Crocodilia, it may further be remarked that diminution of 

 weight would favour crocodilian movements in air, and that a 

 loosely jointed armour would less impede the evolutions required to 

 catch a prey on land. 



In this relation, also, arising out of the introduction, in Tertiary 

 times, of large many species of warm-blooded mammals frequenting 

 the banks of lakes and rivers tenanted by carnivorous Alligators and 

 Crocodiles, I have been led to ponder upon the well-marked dif- 

 ference in the relative position of the 4 palato-nares ' (internal or 

 posterior nostrils, figs. 3&6K) which exists between the Secondary 

 and Tertiary Crocodiles. 



Figs. 1-3. — Cranium of Crocodilus. 



1, Lateral view. 



O. Orbits. 



T. Temporal apertures. 



2. From above. 



P. Ptery go-maxillary 



apertures. 

 N. Palatal nostril. 



3. From below. 



V. Venous foramen. 

 E. Eustachian foramen. 



The physiologist discerns in the soft palatal and gular structures, 

 concomitant with the backward position and small size of the ' palato- 



