We also know that a certain rather small strip of the upper brain-surface, or cortex, about the size of two fingers, running upward and backward from just above the ear, controls the movements of the different parts of the body. One little patch of it for the hand, another for the wrist, another for the arm, another for the shoulder, another for the foot, and so on. We can even pick out the little patch which controls so small a part of the body as the thumb or the eyelids. So when we have a tumor of the brain or an injury to the skull in this region, we can tell, by noticing what groups of muscles are paralyzed, almost exactly where that injury or tumor is. Then we can drill a hole in the skull directly over it and remove the tumor, lift up the splinter of bone, or tie the ruptured blood vessel. Three other patches, or areas, running along the side of the brain, each of them about two inches across, are known to be the centres for smell, hearing, and sight, that for sight lying furthest back. Damage to one of these areas will make the individual more or less completely blind, or deaf, or deprived of the sense of smell, as the case may be. At the lower part of the area which controls the muscles of the different parts of the body, above and a little in front of the tip of the ear, lies a very important centre, which controls the movements of the tongue and lips, and is known as the _speech centre_. If this should be injured or destroyed, the power of speech is entirely lost. This, curiously enough, lies upon the left side of the brain, and is the only one-sided centre in the body. Why this is so is somewhat puzzling, except that as speech is made up both of sound and of gesture, and our gestures are usually made with the right hand, it is not unreasonable to suppose that the speech centre should have grown up on that side of the brain which controls the right hand, which is, as you remember, the left hemisphere. What makes this more probable is that in persons who are "left-handed," the speech centre lies upon the opposite or _right_ side of the brain. So it is waste of time and does more harm than good to try to "break" any child of left-handedness. The Spinal Cord. Running downward from the base of the brain, like the stalk of a flower, is a great bundle of nerve-fibres, the central cable of our body telephone system, the spinal cord. This, you will remember, runs through a bony tube formed by the arches of the successive vertebrae; and as it runs down the body, like every other cable it gives off and receives branches connecting it with the different parts of the body through which it passes. These branches are given off in pairs, and run out through openings between the little sections of bone, or vertebrae, of which the spinal column is made up. They are called the _spinal nerves_, and each pair supplies the part of the body which lies near the place where it comes out of the cord.