certain neurons with the dendrites of other neurons. The
purpose of such connections is to provide the means of communication
between different parts of the body. There appears to be no actual uniting
of the fiber branches with the dendrites, but they come into relations
sufficiently close to establish _conduction pathways_, and these extend
throughout the body (Fig. 129). They connect all parts of the body with
the brain and spinal cord, while connections within the brain and cord
bring the parts into communication with each other.

[Fig. 129]

Fig. 129--*Diagram of a nerve path* starting at the skin, extending through
the spinal cord, and passing out to muscles. A division of this path also
reaches the brain.

*Nature of the Nervous System.*--The nervous system represents the sum
total of the neurons in the body. In some respects it may be compared to
the modern telephone system. The neurons, like the electric wires, connect
different places with a central station (the brain and spinal cord), and
through the central station connections are established between the
different places in the system. As the separate wires are massed together
to form cables, the neurons are massed to form the gross structures of the
nervous system. The nervous system, however, is so radically different
from anything found outside of the animal body that no comparison can give
an adequate idea of it. We now pass to a study of the gross structures
observed in the nerve skeleton.

*Divisions of the Nervous System.*--While all of the nervous structures are
very closely blended, forming one complete system for the entire body,
this system presents different divisions which may, for convenience, be
studied separately. As physiologists have become better acquainted with
the human nervous system, different schemes of classification have been
proposed. The following outline, based upon the location of the different
parts, presents perhaps the simplest view of the entire group of nervous
structures:

[Table]

*The Central Division.*--This division of the nervous system lies within
the cranial and spinal cavities, and consists of the brain and the spinal
cord. The brain occupying the cranial cavity and the spinal cord in the
spinal cavity connect with each other through the large opening at the
base of the skull to form one continuous structure. The b