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THE NERVOUS SYSTEM. 283

over the head, its close relation to other nerves and to the plexuses
and gano;lia of the sympathetic nerve, it becomes involved in nearly
all the diseases of the external portion of the head as well as the
superhcial and deep parts of the face. " The intimate relations which
the nerve beai's with the points of origin of the sixth, seventh, eighth,
ninth, tenth, eleventh, and twelfth cranial nerves in the floor of the
fourth ventricle possibly explain many of those phenomena which are
considered as reflex in character, and whose starting-point seems to
depend upon some irritation of the fifth nerve by means of various
branches" (Ranney). It resembles a spinal nerve, in that it arises by
two roots, anterior and posterior. The posterior root is sensory in
character, and has a ganglion upon it, while the anterior root has no
ganglion and is motor in character.
The large, sensory, or posterior root emerges from a point in close
l^roximity to the centre of the lateral surface of the pons varolii, but
nearer its superior than its inferior border (Fig. 136).
Fig. 143.

Sejtsnry Root
Mo-tor Root-

AwHcuIo-Terajtoral N.

nistribution of the Second and Tliiid Divisions of the Fifth Nerve and Submaxillary Ganglion.
The small, motor, or anterior root is made up of six or eight rounded
filaments (Vulpian), and emerges from the pons a little above the larger
posterior root, being separated from it by a few transverse fibres of