column. 1, The
cerebrum. 2, The cerebellum. 3, The medulla oblongata. 4, 4, The spinal
cord in its canal.]

[Illustration: Fig. 129. Anterior view of the brain and spinal cord. 1,
1, The two hemispheres of the cerebrum. 3, 3, The cerebellum. 4, The
olfactory nerve. 5, The optic nerve. 7, The third pair of nerves. 8, The
pons varolii. 9, The fourth pair of nerves. 10, The lower portion of the
medulla oblongata. 11, 11, The spinal cord. 12, 12, Spinal nerves. 13,
13, The brachial plexus. 14, 14, The lumbar and sacral plexus.]

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755-767. _Give the anatomy of the spinal cord, spinal nerves, and the
sympathetic nerve._ 755. What does the spinal column contain? 756.
Give the extent of the spinal cord. How many enlargements has this
cord? What is said of each enlargement? 757. Into how many parts is
the spinal cord divided? Give the function of these columns.

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758. The SPINAL NERVES, that connect with the spinal cord, are
arranged in thirty-one pairs, each arising by two roots; an anterior,
or _motor_ root, and a posterior, or _sensitive_ root. Each nerve,
when minutely examined, is found to consist of an aggregate of very
delicate filaments, enclosed in a common cellular envelope.

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758. How many pairs of nerves issue from the spinal cord? Explain fig.
128. Fig. 129.

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759. The anterior roots arise from a narrow white line upon the
anterior columns of the spinal cord. The posterior roots arise from a
narrow gray band formed by the internal gray substance of the cord.
They are larger, and the filaments of origin more numerous than those
of the anterior roots. A ganglion is found upon each of the posterior
roots in the openings between the bones of the spinal column through
which the nerve passes.

[Illustration: Fig. 130. A section of the spinal cord, surrounded by its
sheath. B, A spinal nerve, formed by the union of the motor root (C) and
the sensitive root (D.) At D, the ganglion upon this root is seen.]

760. After the formation of the ganglion, the two roots unite, and
constitute a spinal nerve, which passes through the opening between
the vertebrae on the sides of the spinal column. The nerves divide and
subdivide, until their minute filaments ramify on the tissues of the
different organs.

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759. Give the origin of the anterior roots. Of the posterior roots. In
what re