115 



than a distinct function, the vehicle of the im- 

 pression being, not air, but water. 



Such is the case, of course, in all fishes in 

 which the nasal cavities are situated, in general, 

 on the sides of the snout ; and are lined by a 

 plaited membrane, for the distribution of the pro- 

 per nerve. These cavities have, however, no 

 internal opening, so that there can be no perfect 

 current of the fluid through them ; but the dis- 

 tance at which some fishes scent their prey is 

 nevertheless immense. 



In reptiles, the nasal cavities have both an in- 

 ternal and external opening ; the former being, 

 in frogs, turtles and serpents, in the palate, but 

 in lizards, in some of which, as the crocodile, 

 they are exceedingly long, in the pharynx, or mus- 

 cular bag at the back part of the mouth. Most 

 reptiles also, have a kind of moveable lid at the 

 aperture of their nasal cavities, by which they 

 close them when under water ; this medium be- 

 ing apparently but ill adapted, in them, to the 

 function of smell. The proper vehicle of the 

 impression in reptiles, as well as in birds and 

 mammiferous animals, is air ; and this the for- 

 mer draw through their nasal cavities during in- 

 spiration, effected, as I have already explained, 

 by depressing their lingual bone, and thus en- 

 larging the cavity of the mouth. 



In birds, the nasal cavities are in general very 

 large, their external aperture being in the upper 

 mandible, and their internal in the pharynx. The 

 olfactory nerve is very large in carnivorous birds, 



