Here the windpipe ends in the lungs, but the gullet runs straight through the chest, lying close at the back on the backbone, and passes through a hole in the diaphragm into the abdomen, where it swells out into the stomach. Then it narrows again into the intestine, and after winding about inside the cavity of the abdomen a good deal, finally leaves it. You see the =alimentary canal= (for that is the name given to this long tube made up of gullet, stomach, intestine, &c.) =goes right through the cavity of the body without opening into it=--very much as the tall narrow glass of a lamp passes through the large globe glass. You might pour anything down the narrow glass without its going into the globe glass, and you might fill the globe glass and yet leave the narrow glass quite empty. If you imagine both glasses soft and flexible instead of hard and stiff, and suppose the narrow glass to be very long and twisted about so as to all but fill the globe, you will have a very fair idea of how the alimentary canal is placed in the cavity of the body. Besides the alimentary canal, there is in the chest, in addition to the windpipe and lungs, the heart with its great tubes, and in the abdomen there are the liver, the kidneys, and other organs. These two great cavities, with all that is inside them, together with wrappings of flesh and skin which make up the walls of the cavities, form the trunk, and on to the trunk are fastened the jointed legs and arms. These have no large cavities, and the alimentary canal goes nowhere near them. One more thing you have to note. There is only one alimentary canal, one liver, one heart--but there are two kidneys and two lungs, the one on one side, the other on the other, and the one very much like the other. There are two arms and two legs, the one almost exactly like the other. There is only one head, but one side of the head is almost exactly like the other. One side of the vertebral column is exactly like the other--as are also the two halves of the brain and the two halves of the spinal cord. In fact, if you were to cut your rabbit in half from his nose to his tail, you would find that except for his alimentary canal, his heart, and his liver, one half was almost exactly the counterpart of the other. Such is the structure of a rabbit, and your own body, in all the points I have mentioned, is made up exactly in the same way. WHAT TAKES PLACE WHEN WE MOVE. § III. =13.= Let us now go back to the question. =How is it that we can move about as we do?= And first of all let us take one particular movement and see if we can understand that. For instance, you can bend your arm. You know that when your arm is lying flat on the table, you can, if you like, bend the lower part of your arm (the fore-arm as it is called, reaching from the elbow to the hand) on the upper arm until your fingers touch your shoulder. How do you manage to do that?