In the tail of the bird, we find the vertebræ flattened and crowded together into a triangular stump, while the tail of the reptile is extended, pointed, and supple. The reptile has four limbs; in the bird the two front limbs--the hands of the reptile--are changed to wings. The long-toothed jaws of the reptile become the horny beak of the bird. The reptile has scales and the bird has feathers, but there are spots on the reptile bare of scales, and on the bird bare of feathers.[43] The sea had its inhabitants long before the land was populated, and the first vertebrates, the fish, were citizens of the sea. Before the earliest reptiles came, there were amphibians, which lived more readily in the water than on the land; then followed land reptiles, and finally flying reptiles. In like manner, the first birds were chiefly aquatic or swimming birds; then came huge, unwieldy walking birds, and finally flying birds. The earliest birds also diminish the distance between themselves and the reptiles, by the possession of teeth. In regard to feathers, we find that the plumage of the first birds was coarse and scanty, and consisted chiefly of quill feathers. The legs of all birds are covered with true scales such as the reptiles have.[44] When we look at the reptile and the bird, the differences that seem most startling are between the wings of the bird and the fore-feet of the reptile, and between the scales of the reptile and the feathers of the bird. When we find the fossil form of one of the first flying creatures, we see that the huge wings were made of parchment-like skin, stretched upon the arm and fourth finger, which extended in claws in front of the membrane. If we examine that curious flying mammal, the bat, we shall see a similar construction, one finger of the bat’s fore-leg extending beyond the wing into a hooked claw, by which it can hang itself up for rest, or upon which it can walk, going on all fours, in a clumsy fashion. Now, if we take the bones of a bird’s wing, we shall find that it has a large, thick upper bone, corresponding to the upper bone in our own arm; then the next section has two smaller bones, one slightly curved and one straight, to match the bones in our arm from the elbow to the wrist; and then in that small, pointed first section, we find three finger-bones. If we lay all these bones in their order we shall find a very good arm and hand. But now take these bones and construct from them a leg, and we shall notice that any arm is a modified and reduced leg. In nearly all animals the fore-legs are smaller and more symmetrical than the hind-legs. In the reptile family the fore-leg looks very like an arm and hand.