Bats, however, really can fly, and the way in which their wings are made is very curious. If you were to look at a bat's skeleton, you would notice, first of all, that the front limbs were very much larger than the hinder ones. The upper arm-bone is very long indeed, the lower arm-bone is longer still, and the bones of the fingers are longest of all. The middle finger of a bat, indeed, is often longer than the whole of its body! Now these bones form the framework of the wing. You know how the silk or satin of a lady's fan is stretched upon the ribs. Well, a very thin and delicate skin is stretched upon the bones of a bat's arm and hand in just the same way. And when the little animal wants to fly, it stretches its fingers apart, and so spreads the wing. When it wants to rest it closes them, and so folds it against its body. Then you would notice that a high bony ridge runs down the bat's breast-bone. Now such a ridge as this always signifies great strength, because muscles must be fastened at each end to bones; and when the muscles are very large and powerful, the bones must be very strong in order to carry them. So, when an animal needs very strong breast-muscles, so that it may be able to fly well, we always find a high bony ridge running down its breast-bone; and to this ridge the great muscles which work the wings are fastened. Something more is necessary, however, if the animal is to fly properly. It must be able to steer itself in the air just as a boat has to be steered in the water. Otherwise it would never be able to fly in the right direction. So nature has given it a kind of air-rudder; for the skin which is stretched upon the wings is carried on round the end of the body, and is supported there, partly by the hind legs, and partly by the bones of the tail. And by turning this curious rudder to one side or the other, or tilting it just a little up or a little down, the bat is able to alter its course at will. THE USEFUL CLAW But you would notice something else on looking at a bat's skeleton. You would notice that the bones of the thumb are not long and slender, like those of the fingers, but that they are quite short and stout, with a sharp hooked claw at the tip. The bat uses this claw when it finds itself on the ground. It cannot walk, of course, as it has no front feet; so it hitches itself along by means of its thumbs, hooking first one claw into the ground and then the other, and so managing to drag itself slowly and awkwardly forward. It is not at all fond of shuffling along in this way, however, and always takes to flight as soon as it possibly can. But as it cannot well rise from the ground it has to climb to a little height and let itself drop, so that as it falls it may spread its wings and fly away. And it always climbs in a very curious manner, with its tail upward and its head toward the ground, using first the claws of one little foot and then those of the other.