Habits.—The pigeon lives upon grain, which it picks up by means of its horny bill. The length and flexibility of the neck are a great help in feeding. The food is swallowed immediately and passed into a large bag called the crop, which is really a dilatation of the lower part of the gullet. Here it is macerated for some time before it passes onward to the true stomach. The hinder part of the stomach is called the gizzard; it has very thick walls and a hard horny lining. In the gizzard the food is ground up by the aid of small stones which the pigeon swallows for the purpose. The stomach is followed by a much-coiled intestine, in which the process of digestion is completed. The pigeon differs from many birds in walking instead of hopping. When perching, it bends its legs at the ankles, an action which automatically closes the toes in such a manner that the perch is grasped behind by the first toe and in front by the second, third, and [Pg 272] fourth. The weight of the body is sufficient to maintain a tight clasp upon the perch, so that the bird is able to sleep comfortably in this position. Fig. 179.—A Falcon. The regions of a bird’s body. The hen-pigeon lays two white eggs, which are sat upon by the [Pg 273] parents for fourteen days and thereby kept at a temperature of about 40 degrees Centigrade. The young birds then break through the shell and are hatched. As the chicks are at first quite helpless and unable to feed themselves, the parents supply them with a milky fluid secreted by their crops. This is sometimes called “pigeon’s milk.” Newly hatched pigeons are covered with fine feathers called down, which are pushed off by the development of the permanent feathers beneath them. The nests of wood-pigeons (Fig. 180) are usually built in trees; they are somewhat rough structures, composed of twigs, and open at the top. Fig. 180.—Wood-pigeon’s nest. The wings.—A bird’s wings are full of interest, from whatever point of view they are considered. Even now, the exact manner in which they and the tail are used to bring about the many different movements of flight is not fully understood; but a general idea may be obtained by an examination of the bones and feathers and the careful observation of flying birds. [Pg 274] Fig. 181.—The skeleton of the limbs and tail of a flying-bird. OA, bone of upper arm; OS, bone of upper leg; Rd, Ul, bones of fore-arm; T, Fi, bones of leg; HW, MH, bones of wrist; F, F, F, bones of fingers; Z, Z, Z´, MP, bones of foot; Scp, shoulder blade; Cr, keel on sternum (St); Pg, ploughshare bone.