424 



PROF. R. OWEN ON THE MODIFYING INFLUNCE 



nares/ in the existing Crocodiles and Alligators of Asia, Africa, and 

 America, the power of holding submerged a powerful mammiferous 

 quadruped, without permitting the streams of water traversing the 

 great cavity of the mouth during the struggle to get access to the 

 posterior nostrils and wind-pipe of the amphibious assailant. 



The valvular mechanism applicable to, or, I may say, possible 

 with, the peculiar position of the posterior nostrils of procoelian 

 Crocodiles, opening vertically behind the bony palate, not hori- 

 zontally upon that plane, could hardly be adjusted to the relatively 

 larger postpalatine apertures, upon a horizontal plane at some 

 distance from the occiput, with the inner nostril opening at a more 

 advanced position in the mouth — an arrangement which charac- 

 terizes all amphicoelians. 



Pigs. 4-6. — Cranium of Teleosaurus. 



4 





v ""^lalB^^* 



wrr- "y ' — 





^'wjD^^K 





4. Lateral view. 



5. From above. 



6. From below. 



Explanation of letters as under figs. 1-3. 



No doubt there were sphincteric structures which would exclude 

 water from the glottis in all the aquatic air-breathing reptiles; but the 

 peculiar and well- developed valvular contrivances to that end in 

 existing crocodiles are conditions of the relative size and position of 

 the posterior nostrils in them, and the repetition of that character 

 in the palato-nares of all known Tertiary crocodiles justifies an in- 



