The flesh of animals is by common consent divided into three principal classes, namely, the flesh of terrestrial mammals, or animals not provided with wings; second, aerial animals, or animals provided with wings, and, third, aquatic animals. A very common classification of these three kinds of food is flesh, fowl, and fish. There are animals, the flesh of which is eaten by many, which are not exactly included in this classification; for instance, animals of an amphibious nature, living partly on land and partly on sea. Also many of the animals classed as aerial live chiefly upon the earth; although having wings they do not use them, such as domesticated fowls. This classification, however, is sufficiently exact for the practical purposes of a food manual and, therefore, under the head of meat is included the edible flesh of mammals living on the land. =Animals Whose Flesh is Edible.=--Probably the only complete classification of this kind would be to include every animal living on the face of the earth since, perhaps, the flesh of every animal living has been more or less eaten by man. In a civilized community, however, except in times of disaster and dire necessity, certain classes of animals only furnish the principal meat food. Nearly all the meat food consumed in the United States is derived from cattle, sheep, and swine. Goat flesh is eaten only to a limited extent and horse meat scarcely at all, and the only other meats of importance are those of wild animals. The principal wild animals used for food are the deer, bear, rabbit, and squirrel. Many other wild animals, however, are eaten and in some cases highly prized. In this manual only the principal meat foods both of domesticated and wild animals will be mentioned. =Classification of Meat Food as Respects Age.=--The edible flesh of domesticated animals as well as of wild animals is eaten both in the young and full-grown state. Common names, however, designate these different classes. For instance, veal in the growing and beef for the full-grown animal, lamb for the young and mutton for the full-grown sheep, pig in the younger and pork in the full-grown swine, etc. There is no legal limit of age for such a distinction, but as long as the animal is not fully grown it may be classified under the name representing the young animal. There is a common understanding, however, that in the case of veal and lamb the animal must be under one year of age and usually not under two nor more than eight months of age. A classification of this kind is so indefinite, however, that no strict definition can be given other than that founded on the general principles above outlined.