In keeping
with these functions, the two divisions of the nerve are made up of
different kinds of fibers, as follows:
1. The dorsal-root divisions, of the fibers of di-axonic neurons, the
cell-bodies of which form the dorsal-root ganglia (Fig. 135).
2. The ventral-root divisions, of the fibers of mon-axonic neurons, the
cell-bodies of which are in the gray matter of the cord.
The first convey impulses to the cord and are called _afferent_
neurons;(102) the second convey impulses from the cord and are known as
_efferent_ neurons. Thus, by forming a part of the nerve pathways between
the skin and the brain, the dorsal divisions of these nerves aid in the
production of feeling; and by completing pathways to the muscles, the
ventral divisions aid in the production of motion (Figs. 129, 135, and
141).
[Fig. 135]
Fig. 135--*Connection of spinal nerves with the cord.* On the right is
shown a nerve pathway from the skin to the muscle. A division of this
pathway reaches the brain.
*The Cranial Nerves.*--From the under front surface of the brain, twelve
pairs of nerves emerge and pass to the head, neck, and upper portions of
the trunk. These, the cranial nerves, have names suggestive of their
function or distribution and, in addition, are given numbers which
indicate the order in which they leave the brain (Fig.
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