These joints of the bones are so contrived that they do not wear out. They work nicely through a long life. Now it would be very strange if a joint in a machine should work all the time for seventy or eighty years, and still be almost as good as new. No man ever made such a joint.
The oiling of them.
You know that men keep oiling the joints in machinery. If they did not, the joints would soon wear out. When the cars stop at a station, you see men with tin vessels oiling the boxes of the wheels of the locomotive and the cars, and other parts that rub on each other. The joints of our bones need no such care from us. We never need to oil them as men oil machinery. They are very nicely made. The ends of the bones are tipped with a very smooth substance, and this is always kept in good order; and then, too, the joints always keep themselves oiled. How this is done I explain in a book for older scholars.
The bones are the frame-work of the body. They are to the body what whalebones are to an umbrella, what timbers are to a house, or what the ribs of leaves are, as I told you in Part First, to the leaves. The bones make the body firm. You could not stand up if you had no bones; you would have to crawl like the worm. See one bracing himself to pull or push. The bones are all pressed tightly against each other by the strong muscles.
The bones of the body have very different shapes and sizes. Let us look at some of them.
Bones of the head.
The bones of the head, represented here, make a roundish box. This is to hold the brain. Here the mind, the governor of all the machinery of the body, resides. Great care is therefore taken to guard well this upper room of the body. Its bony walls are made very strong.
