It would be strange indeed if we did not care to know something about our own home; but our body is not only the house in which we live, it is also the means, through those five senses--the eye, the ear, and the organs of touch, taste, and smell--which have been so well called "the five gateways of knowledge," by which we learn all that can be known by us of the world outside us. More than this, it is the wonderfully perfect instrument, and implicitly obedient servant, by which all that we do is performed. But the science that teaches us all that is known about our bodies is a very difficult study, and there are many hard names to master, even at the very outset. For instance, when we speak of the bony framework--that skeleton which, as you know, belongs to us in common with the vertebrate animals--there is a great deal which you would find very difficult to remember. Still, as I daresay you have found out, the more we learn, even of difficult sciences, the more we _can_ learn, and little May (though, to be sure, she is now four years older than she was when you first made her acquaintance) _has_ learnt a good many of the hard words. She could show you upon her own round arm, just where the bone which reaches from the shoulder to the elbow begins and ends, and tell you its name, and the names of the two bones which reach from the elbow to the wrist, and of the wrist-bones, and of those which you can feel in the palm of your hand, and the finger-bones. But when you hear that you have more than two hundred bones in your body, you will be inclined to agree with me that it would take both of us some time to learn even their names, much more to know all about them. The spine consists of twenty-four short bones, each with a little ring. These vertebras are piled up one upon the other; for God has made our bodies upright; our faces, are lifted upwards, and our eyes look straight before us. These twenty-four little bones are closely and strongly bound together, and between each one and its neighbour there is something so soft and elastic that we can bend our heads, or move in any direction, without the slightest strain or jar. The head is most wonderfully built up, like an arch, of several bones beautifully joined in a very strong and perfect way which carpenters call "dove-tailing." We can understand why the head, which is so much exposed, and is almost entirely occupied by the brain, should be so carefully protected; for thought, memory, will, and what we can best express as "consciousness of our being," all depend upon it. Passing from head to foot, we find that our feet, which are not large, yet must bear the weight of the body, are also made upon the arch-principle, which has been found, like the hollow bones of the bird's wing, to combine lightness and strength. The twenty-six bones are so fitted together that this wonderful arch is quite elastic, as you can prove by moving your own foot up and down.