Page:Quarterly Journal of the Geological Society of London, vol. 35.djvu/203

Rh Admitting, for Mr. Hulke's argument, that the outer nostrils of a Crocodile, with their dense tegumentary boundary, could, like those of a seal, be shut by the action of a sphincter, exclusion by such narial opening of the watery element would not affect its entry by the mouth forced open by the seized and struggling mammal.

The question is, supposing the water to be stopped out of the anterior aperture, how is it to be excluded from the posterior one of the narial canal and at the same time from the entry of the wind-pipe?

And here comes the point for consideration in the comparison of Mesozoic and Neozoic Crocodiles with relation to their enemies and their prey.

In all the Crocodiles contemporary with "large mammals" there is a double valvular structure at the back of the mouth which prevents the water that may fill and be flowing through the mouth from getting into either the hinder nostril or into the glottis. One valve is fleshy and membranous; it hangs from the hind part of the palate, and answers to our "velum palati:" the other valve is peculiarly Crocodilian, at least in size and shape; 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 back nostril it is situated; it may be compared to a broad epiglottis, shutting off the glottis from the mouth.

To make this complex mechanical structure available, the back nostril is singularly reduced in size, and such reduction is shown in the skull. The small relative palato-narial orifice in procœlian or Neozoic Crocodilia is truly striking when contrasted with the size of the palato-nares in lizards and in amphicœlian or Mesozoic Crocodilia.

But this is not the only character or condition of the procœlian palato-naris which renders the adaptation of the valvular machinery available for its purpose. In Neozoic Crocodiles the palato-naris is placed far back—further back than the basihyal—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.

What the modifications of the soft soluble parts of the hyoid and