THE CEREBRO-SPINAL SYSTEM OF NERVES. 633 
cause trismus (locked-jaw) from tonic tetanic action of the mus- 
cles of mastication supplied by this nerve. 2. Paralysis of the 
same muscles may ensue from degeneration of the motor nuclei 
or pressure on the nerve in its course. 3. Neuralgia of any of 
the sensory branches may occur from a great variety of causes, 
and often maps out very exactly the course and distribution of 
the branches of the nerve. 4. Vaso-motor disturbances are not 
infrequently associated with neuralgia. Blushing is an evi- 
dence of the normal action of the vaso-motor fibers of the fifth 
nerve. 5, A variety of trophic (metabolic) disturbances may 
arise from disorder of this nerve, its nuclei of origin or its gan- 
glia, such as grayness and loss of hair (imperfect nutrition), 
eruptions of the skin along the course of the nerves, etc. Atro- 
phy of the face, on one or both sides, gradual and progressive, 
may occur. Such affections, as well as others, point in the most 
forcible manner to the influence uf the nervous system over the 
metabolism of the body. 
The Glosso-pharyngeal or Ninth Nerve.—This nerve, together 
with the vagus and spinal accessory, constitutes the eighth 
pair, or rather trio. Functionally, however, they are quite dis- 
tinct. 
The glosso-pharyngeal arises in the floor of the fourth ven- 
tricle above the nucleus for the vagus. Itis a mixed nerve 
with efferent and afferent fibers: 1. Efferent fibers, furnishing 
motor fibers to the middle constrictor of the pharynx, stylo- 
pharyngeus, levator palati, and asygos uvule. 2 Afferent 
fibers, which are the paths of sensory impulses from the base 
of the tongue, the soft palate, the tonsils, the Eustachian tube, 
tympanum, and anterior portion of the epiglottis. Stimulation 
of the regions just mentioned gives rise reflexly to the move- 
ments of swallowing and to reflex secretion of saliva. 
This nerve is also the special nerve of taste to the back of 
the tongue. 
The Pneumogastric, Vagus, or Tenth Nerve.—Most of the func- 
tions of this nerve have already been considered in previous 
chapters. 
In some of the. lower vertebrates (sharks) the nerve arises 
by a series of distinct roots, some of which remain separate 
throughout. This fact explains its peculiarities, anatomical 
and functional, in the higher vertebrates. In these there have 
been concentration and blending, so that what seems to be one 
nerve is really made up of several distinct bundles of fibers, 
many of which leave the main trunk later. 
