its filaments (_b, c, d, e_.)]

In the brain and spinal cord the nerve-fibers often terminate in minute
masses of a gray or ash-colored granular substance, termed _ganglia_, or
_ganglionic corpuscles_.

The ganglia are cellular corpuscles of irregular form, and possess
fibrous appendages, which serve to connect them with one another. These
ganglia form the cortical covering of the brain, and are also found in
the interior of the spinal cord. According to Kölliker, the larger of
these nerve-cells measure only 1/200 of an inch in diameter. The brain
is chiefly composed of nervous ganglia.

Nerves are classified with reference to their origin, as
_cerebral_--those originating in the brain, and _spinal_--those
originating in the spinal cord.

There are two sets of nerves and nerve-centers, which are intimately
connected, but which can be more conveniently studied apart. These are
the _cerebro-spinal_ system, consisting of the cerebro-spinal axis, and
the cerebral and spinal nerves; and the _sympathetic_ system, consisting
of the chain of sympathetic ganglia, the nerves which they give off, and
the nervous trunks which connect them with one another and with the
cerebro-spinal nerves.


THE CEREBRO-SPINAL SYSTEM.


THE CEREBRO-SPINAL AXIS consists of the brain and spinal cord. It lies