The long slim part above the toes, what we call the leg, is named in the books the "tarsus." The tarsus is generally bare, with a leathery skin; but in some hawks and owls it is covered with feathers. Birds who live away up in the cold have feathers down on to the toes. On looking carefully at one of these bare legs, it will be seen that it is not smooth like a lead pencil. It is marked in a sort of pattern. Different species of birds show different patterns. Some look like the shingles on a roof; others like little squares or plates; and some are finer, like scales on a tiny fish. These marks help in arranging birds in the books. That is, all who have the same pattern are said to be related. The legs of birds are not all of the same length for their size. Some who never go about on the ground, like hummingbirds, swallows, and swifts, have very short legs. Birds who walk and hop on the ground have them longer, and birds who wade in the water have the longest of all. XXV HIS WINGS AND TAIL A BIRD'S wing does not look much like our arm and hand, yet the bones show that they are the same. The bird has a shoulder, elbow, and wrist, as we have. He even has fingers, though they are so covered up by feathers that one would never know it. He has not so many fingers as we have, and they are not movable like ours. A bird's wing is a wonderful flying-machine, which men have been trying to imitate these many years. It is made of long stiff feathers, which fold down smoothly over one another at his side when he is resting, but can spread in an instant into a broad fan, to beat the air and carry him away. One would not think that feathers could have so much power; but when the wing is spread, the barbs of the feathers hook together with tiny hooks, so small a microscope is needed to see them; and that, together with the edges lapping over each other, makes them almost like one solid surface. Wings are not alike in shape. The wing of a swallow is long and narrow, while that of a hen or grouse is short and round. We can tell by the shape of a wing how a bird flies. A long, narrow, pointed wing shows that the bird has an easy, skimming flight,--either he flies great distances, or spends hours at a time on wing (Fig. 11). [Illustration: FIG. 11. Wing of Swift.] The short round wing (Fig. 12) shows that a bird has a strong flight for short distances. These wings are found mostly on rather heavy birds, like grouse. [Illustration: FIG. 12. Wing of Sparrow.] The longest wings are seen on water birds, such as the petrel and the frigate-bird. The shortest, also, are found among water birds, those who swim more than they fly, as the auks. All the feathers of the wing are named, and it will be well to remember that the long stiff quills are called _remiges_ or "rowers." These are firmly rooted in the flesh, and are the hardest to pull out. They are the most important to the safety of the bird.