640 BRITISH FOSSIL REPTILES. 



tions, to their augmentation of size, and he would set it down as one of the factors in 

 the progressive transmutation of a Teleosaur into an AHigator. 



His opponent would ask, of course, for the transitional forms. The subjects of the 

 foregoing pages (631 — 636) in some degree represent such. 



Those which I next proceed to describe also suggest relations of adjustment of 

 characters to associated, probable, prey. Before entering on the descriptive details I 

 may revert to the topic last discussed. 



A large and powerful modern Crocodile having seized and submerged a tiger or 

 bufiido, admits the water of the river it haunts into its wide lipless mouth by the spaces 

 to which the thickness of the part of the prey gripped keeps asunder the upper and the 

 lower jaws. Thus, the part of the mouth not occupied by the prey is filled with the 

 fluid in which the mammal is being dragged and drowned. " The closure of the exterior 

 nostrils "^ would not prevent the water entering the ' glottis.' A special arrangement 

 is requisite for this purpose, and such arrangement, as it exists in Neozoic Crocodiles, 

 is incompatible with the relative position of " the posterior nares" and the glottis in the 

 Mesozoic Crocodiles. The question is, with a closure of the external nostrils and the 

 exclusion of water admitted by the mouth into the nasal passage, how is the water to be 

 prevented from getting into the windpipe? We know how this is eflfected in the 

 Cetaceans ; and modern Crocodiles have as efficient a mechanism to the same end though 

 on a different plan, but requiring a size and position of the palatonares which, as shown 

 in previous pages, constitutes one of the best marked cranial characters differentiating the 

 Mesozoic and Neozoic CrococUlia. 



In all the Crocodiles contemporary with "large and active mammals "^ there is a 

 double valvular structure at the back of the mouth, which prevents the water having 

 access to the mouth, from entering either the hinder nostril or the glottis. A mem- 

 branous and fleshy fold hangs, like a curtain, from the hind border of the I'oof of the 

 mouth, and answers to our ' velum palati :' the other valve is peculiarly crocodilian ; it is 

 a broad, gristly plate, which rises from the root of the tongue, carrying with it a covering 

 of the lingual integument ; and, when the palatal valve is applied to it, they form 

 together a complete partition wall, closing the back of the mouth, between which and 

 " the posterior nares " it is situated, shutting off both the latter aperture and the glottis 

 from the mouth. 



To make this mechanism available, the hind nostril is reduced in size, and such 

 reduction is shown in the skull. The palatonaris is also placed far back, and its plane 

 instead of being horizontal is tilted up at the angle which makes the operation of the 

 two parts or folding doors of the partition most effective in closing the oral chamber 

 posteriorly.^ If the submergence of the Crocodile, with its large mammalian prey, 



I 'Quart. Joiirn. of Geol. Soc.,' May, 1S78, p. 429. 



- Loc. cit., p. 425. 



3 ' Proceedings of the Zool. Soc.,' October 2.5th, 1S31, p. 139. 



