The head, again, is unlike all these. Indeed, you will not understand how the head is made unless you take a rabbit’s skull and place it side by side with the rabbit’s head. If you do this, you will at once see how the mouth and throat are formed. =You will notice that the skull is all in one piece=, except a bone which you will at once recognize as the jawbone, or, to speak more correctly, the lower =jawbone=; for there are two jawbones. Both these carry teeth, but the upper one is simply part of the skull, and does not move; the lower one does move; it can be made to shut close on the upper jaw, or can be separated a good way from it. The opening between the two jaws is the gap or gape of the mouth, which as you know can be opened or shut at pleasure. If you try it on yourself you will find that, as in the rabbit, it is the lower jaw which moves when you open or shut your mouth. The upper jaw does not move at all except when your whole head moves. Underneath the skull at the top of the neck the mouth narrows into the throat, into the upper part of which the cavity of the nose opens. So that there are two ways into the throat, one through the mouth and the other through the nose (Fig. 2). At the back of the skull you will see a rounded opening, and if you put a bodkin through this opening you will find it leads into a large hollow space in the inside of the skull. In the living rabbit this hollow space is filled up with the =brain=. The skull, in fact, is a box of bone to hold the brain, a bony brain-case. This bony case fits on to the top of the vertebræ of the neck in such a way that the rounded opening we spoke of just now is placed exactly over the top of the tunnel or canal formed by the rings or arches of the vertebræ. If you were to put a wire through the arch of the lowest vertebra, you might push it up through the canal formed by the arches of all the vertebræ, right into the brain cavity. In fact the brain-case and the row of arches of the vertebræ form together one canal, which is a narrow tube in the back and in the neck, but swells out in the head into a wide rounded space (Fig. 2, A and B, _C.S._) During life this canal is filled with a peculiar white delicate material, which is called =nervous matter=. The rounded mass of this material which fills up the cavity of the skull is called the =brain=; the narrower, rod-like, or band-like mass which runs down the vertebral canal in the neck and back is called the =spinal cord=. They have separate names, but they are quite joined together, and the rounded brain tapers off into the band-like cord in such a way that it is difficult to say where the one begins and the other ends.