[Scand.] The appendage of the body of a bird or insect, by means of which it flies. The framework of the bird's wing is formed of a set of bones corresponding to those of the human arm and hand, but having only one perfect finger, corresponding to the index finger; and stretched over this framework is a thin covering of flesh and muscle from which grow the quills and smaller feathers, and these when spread out make up the broad wing. The upper surface is rounded, and the air can easily slide from its edges as it mounts in the air. Bats are the only mammals which fly, and their wings are arms and fingers lengthened out, and supporting a skin spread out like the cover of an umbrella on its ribs. There are other mammals, like the flying squirrel, the flying lemur, etc., which have a partial power of flight. The wings of insects are thin, often transparent, membranes. Some insects use them for only a brief period of their lives ; the ants, after their marriage flight, cast off their wings and live without them afterwards. Some, as the flies, have two wings, but most insects have four.