COMPARATIVE ANATOMY. 
129 
stances, in which the animal has plunged her bill, she 
draws, by the action of her lungs, through the narrow in¬ 
terstices which lie between these teeth; catching, as the 
stream passes across her beak, whatever it may happen to 
bring along with it, that proves agreeable to her choice, 
and easily dismissing all the rest. Now, suppose the pur¬ 
pose to have been, out of a mass of confused heterogene¬ 
ous substances, to separate for the use of the animal, or 
rather to enable the animal to separate for its own, those few 
particles which suited its taste and digestion; what more 
artificial, or more commodious instrument of selection, 
could have been given to it, than this natural filter?* It has 
been observed, also, (what must enable the bird to choose 
and distinguish with greater acuteness, as well, probably, 
as what increases its gratification and its luxury,) that the 
bills of this species are furnished with large nerves, that 
they are covered with a skin,—and that the nerves run 
down to the very extremity. In the curlew, woodcock, and 
snipe, there are three pairs of nerves, equal almost to the 
optic nerve in thickness, which pass first along the roof of 
the mouth, and then along the upper chap, down to the 
point of the bill, long as the bill is. [PI. XXIII. fig. 1.] 
But to return to the train of our observations.—The sim¬ 
ilitude between the bills of birds and the mouths of quad¬ 
rupeds, is exactly such as, for the sake of the argument, 
might be wished for. It is near enough to show the con¬ 
tinuation of the same plan; it is remote enough to exclude 
the supposition of the difference being produced by action 
or use. A more prominent contour, or a wider gape might 
be resolved into the effect of continued efforts, on the part 
of the species, to thrust out the mouth, or open it to the 
stretch. But by what course of action, or exercise, or en¬ 
deavour, shall we get rid of the lips, the gums, the teeth; 
and acquire, in the place of them, pincers of horn? By 
what habit shall we so completely change, not only the 
shape of the part, but the substance of which it is compos¬ 
ed? The truth is, if we had seen no other than the mouths 
of quadrupeds, we should have thought no other could have 
been formed: little could we have supposed, that all the 
purposes of a mouth furnished with lips, and armed with 
* There is a remarkable contrivance of this kind in the genus balcena , 
or proper whale. Numerous parallel plates of the substance called 
whalebone, cover the palatine surface of the uper jaw, and descend ver¬ 
tically into the mouth; the lower edges are fringed by long fibres, which 
serve the animal, when taking in the water, to retain the mollusc®, 
with which the water abounds, and which constitute its food.— Paxton. 
