To begin at the top, the _skull_ is a box of strong, plate-like bones, which have hardened to protect the brain as it grew; and the shape of its upper, or brain, part is exactly that of the head, as you can easily feel by laying your hands upon it.

Then come bony shells, or sockets, for the eyes and nose; and, below these, two heavy half-circles of bone, like the jaws of a steel trap, to carry the teeth.
The thickness of the lower jaw and the size and squareness of the angle where it bends upward to be hinged to the skull, below the ear, are what give the appearance of squareness and determination to the faces of strong, vigorous men or women.

If we want to imply that a person has a feeble will, or weak character, we say he has a "weak jaw." The skull rests upon the top of the backbone, or _spinal column_, which, instead of being one long solid bone, is made up of a number of pieces, or sections, known as _vertebrae_.

Each one of these vertebrae has a ring, or arch, upon its back.

These, running one after the other, form a jointed, bony tube to protect the _spinal cord_, or main nerve-cable of the body, which runs through it.
[Illustration: THE SPINAL COLUMN _V_, vertebra; _C_, cartilage protecting spinal cord; _A_, point of articulation on the right side.] Although the backbone can bend forward or backward, or twist from side to side a little, by the little pieces of bone of which it is built up gliding and turning upon one another, it is really very stiff and rigid, so as to protect the spinal cord and prevent its being stretched or pinched.