Page:Natural History, Birds.djvu/19

6 especially the tarsal portion, which is never applied to the ground in the action of walking.

Though many birds feed on hard substances, their jaws are entirely destitute of teeth; but are more or less extended into two mandibles, and incased in horny coverings of considerable density, which are exceedingly diversified in form and use. "Thus in birds of prey [the beak] well executes the office of a dissecting knife; in seed-eating birds it forms a pair of seed-crackers for extricating the kernel from the husk which envelopes it; in the Swallows and Goat-suckers it is a fly-trap; in the Swans, Geese, and Ducks, it is a flattened strainer, well furnished with nerves in the inside for the detection of the food remaining after the water is strained, by that particular operation which every one must have observed a common duck perform with its bill in muddy water. In the Storks and Herons we find it a fish-spear; and in the Snipes and their allies it becomes a sensitive probe, admirably adapted for penetrating boggy ground, and giving notice of the presence of the latent worm or animalcule." The stomach in Birds consists of three parts (which are not, however, in all cases distinctly developed); the crop or craw, the membranous stomach or proventriculus, and the gizzard. The last, which is seen to advantage in the grain-eating birds, is composed of two very