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.
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