EXTERNAL ANATOMY. NOSTRILS. 57 
completely concealed by a dense tuft of stiff setaceous 
feathers : both these peculiarities may have something of 
the same effect, though produced in a different manner 
to what we have just stated; while the care with which 
nature has defended the nostrils of these birds is for the 
double purpose of preventing their being injured by the 
claws of insects, and to exclude every particle of wood, 
which the bird scatters about whifc perforating and 
breaking into the tree where he knows his food lies 
concealed. In proportion as birds partake both of a 
Vegetable and an insect diet, so are these bristles more 
or less developed. In the robin, for instance, they are 
short and feeble, intimating that its diet is only partially 
insectivorous, or rather, that it seldom captures flying 
insects : and such we know to be tlie fact. Proceeding 
a step further, we find tlie bristles of the thrush and 
Wackbird altogether rudimentary, leading us to suppose 
that, although they may occasionally eat insects, tliey 
never capture them when upon the wing. Experience 
confirms this theoretical inference, for every field natu- 
ralist is fully aware tliat such is truly the fact. 
(56'.) The different forms of the nostrils, no less than 
their situation, deserve attention; for in both these parti- 
culars they assume many different appearances. In all 
the birds of prey, they are situated nearly in the midiUe 
° ^ naked and soft skin, called the cere, which covers 
t e base of both mandibles, and is probably connected 
With the sense of smell. The cere, however, is not con- 
fined to the rapacious tribes; for we find it, although 
much smaller, in almost the whole of the parrot family, 
whose food is entirely vegetable. No other land birds 
possess this appendage; nor can it be said to exist, under 
the same form, in any other birds excepting some of the 
rasorial orders; most of the cranes, herons, &c. have 
the space between the eye and the bill naked and soft; 
ut this is merely from tlie ordinary skin being destitute 
n feathers. The nostrils are either placed, 1. at the 
ase of the lateral surface of the bill, as in the generality 
