The head, the brain, is the initiative centre of our actions; and it is also the receptive centre of our sensations. From it all the various motions of the body are originated; and to it the manifold impressions of the senses are communicated. By two sets of nerves, as by two sets of telegraphic wires, this twofold communication with the head, as the central office, the seat of government in the human frame, is maintained. By the one set, the brain, the thinking, planning, originating power, transmits its orders to the furthest member; the order is received; the muscle contracts; the joint is moved; and the hand holds, or the foot walks. By the other set, the reverse process is carried on; the grasp which presses the hand, the rays which strike the eye, the pulsations which beat on the ear, all these are transmitted to the centre, and the corresponding sensation is thereby and there produced.