little piece of the brain under a microscope, we should find that it is
made up of a great number of very small objects called _nerve_ or
_brain cells_. In the illustration you can see some of these brain
cells.

[Illustration: BRAIN CELLS.]

~5. The Nerves.~--Each cell has one or more branches. Some of the
branches are joined to the branches of other cells so as to unite the
cells together, just as children take hold of one another's hands. Other
branches are drawn out very long.

~6.~ The long branches are such slender threads that a great number of
them together would not be as large as a fine silk thread. A great many
of these fine nerve threads are bound up in little bundles which look
like white cords. These are called _nerves_.

~7.~ The nerves branch out from the brain through openings in the skull,
and go to every part of the body. Every little muscle fibre, the heart,
the stomach, the lungs, the liver, even the bones--all have nerves
coming to them from the brain. So you see that the brain is not wholly
shut up in the skull, because its cells have slender branches running
into all parts of the body; and thus the brain itself is really in every
part of the body, though we usually speak of it as being entirely in the
skull.

~8. The Spinal Cord.~--There are a number of small holes in the skull
through which the nerves pass out, but most of the nerves are bound up
in one large bundle and pass out through an opening at the back part of
the skull and runs downward through a long canal in the backbone. This