CROCODILES. 49 



arrangement of folds produced by the tongue 

 and the velum palatinum, completely shut off 

 from the mouth. Thus, though the mouth may 

 be filled with water, the animal can breathe with 

 impunity, by simply thrusting the tip of the snout 

 above the water, which would not be possible if 

 the posterior apertures of the nostrils opened in 

 their usual place. 



This peculiar arrangement, be it noted, is not 

 an institution of yesterday, but the result of a 

 slow series of changes, which took ages of geo- 

 logical time to accomplish. The remains of the 

 ancient Crocodiles of the Jurassic period show 

 that in them the change had already begun. 

 From thence onwards to the Cretaceous, the 

 completion of this important passage was slowly 

 pushed forwards to its final accomplishment. 



The position of the external nostrils, to which 

 reference has been made, is obviously the result 

 of a more perfect adaptation to aquatic life. If 

 a living specimen be examined it will be noticed 

 that these apertures are seated at the extreme tip 

 of the snout, and directly raised above its surface. 

 They can be closed at will, so as to exclude the 

 water, when the animal is completely submerged, 

 whilst from their peculiar position they enable 

 the animal to breathe, so long as they can obtain 

 air, even while the rest of the body is below the 

 surface, and the mouth open, since the water 

 is excluded from the air passage at the back of 

 the throat by the mechanism just described. 



The old Jurassic Crocodiles have revealed yet 

 other important facts which throw light upon the 

 course of the evolution of their descendants, 

 D 



