"A bird is an instrument working according to a mathematical law," wrote da Vinci. "It lies within the power of man to make this instrument with all its motions, but without the full scope of its powers; but this limitation only applies in respect to balancing itself. Accordingly we may say that such an instrument fabricated by man lacks nothing but the soul of man."
And he gave us instructions, as though to his assistants: "You will make an anatomy of the wings of a bird together with the muscles of the breast which are the movers of these wings. And you will do the same for a man, in order to show the possibility, that there is in man who desires, to sustain himself amid the air by the beating of wings."