commissure. There are certain centres in the spinal cord that are capable
of carrying on certain reflex actions independent of the chief centre in
the brain. The white matter of the cord is made up of paths over which
impulses to and from the brain are transmitted.

_There are twelve pairs of cranial nerves_. Two pairs belong exclusively to
the special senses, smell and sight. Altogether there are ten pairs that
are devoted to functions connected with the head, either as nerves of the
special senses or in a motor or sensory capacity (Figs. 26 and 27). There
are two pairs distributed to other regions. These are the tenth and
eleventh pairs. The tenth pair or pneumogastric is distributed to the vital
organs lodged within the body cavities.

There are forty-two or forty-three pairs of spinal nerves given off from
the spinal cord. The spinal nerves have two roots, superior and inferior.
The superior is the sensory root and the inferior is the motor root, both
uniting to form a mixed nerve trunk. The sensory root possesses a ganglion
from which it originates.

Generally speaking, the cerebrospinal system deals with the special senses,
movement of skeletal or voluntary muscles and cutaneous and muscular
sensations. In addition to the above there is a distinct system termed the
sympathetic. The _sympathetic system_ consists of a long cord, studded with
ganglia, extending from the base of the neck to the sacrum. The ganglia are
connected with the inferior roots of the spinal nerves. This cord is
connected with groups of ganglia and nerve fibres in the abdominal region,
and this in turn is connected with terminal ganglia in distant tissues.
This system of nerves is distributed to the vital organs of the body.

[Illustration: FIG. 26.--Unilateral facial paralysis caused by injury to