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THE yERVOVS SYSTEM. — 313

one passes to the upper portion of the posterior third of the tongue, and
breaks up into numerous branches which supply the circunivallate pa-
pilhe and mucous membrane over this region, extending back as lar as
tlie anterior surfiice of the epiglottis. The smaller branch extends for-
ward to the posterior half of the side of the tongue and interlaces with
the lingual nerve. It supplies the mucous membrane of this portion
of the tonyi-ue.

Pneumogastric Nerve.
The pneumogastric or tenth nerve (nervus vagus, par vagum, or sec-
ond trunk of eighth nerve, according to Willis) (Fig. lo2) at its origin
is purely a sensory nerve, but through its communication with at least
five motor nerves it takes on motor functions, and distributes both sen-
sory and motor iilaments to different organs and tissues. It is the most
widely distributed of all the cranial nerves, having more communicat-
ing branches. Its general distribution is to the pharynx, cesophagUs,
stomach, and alimentary canal, the larynx, trachea, heart, and blood-
vessels. It is thus intijiiately connected with the digestive, respiratory,
and circulatory systems.
Its superficial or aj)parent origin is from the anterior surface of the
upper portion of the medulla oblongata, between the olivary and resti-
form bodies, and also innnediately between the glosso-pharyngeal and
the spinal accessory nerves. It is made up of from fifteen to twenty
filaments, which unite and form a flattened band. It passes transversely
outward across the flocculus to the middle compartment of the posterior
lacerated foramen, through which it makes its exit from the l)rain-case.
It is enclosed with the spinal accessory nerve in a single sheath made up
of dura mater and arachnoid membrane, and is separated from the glosso-
pharyngeal nerve by fibrous and occasionally by osseous tissue.
The ganglia of the pneumogastric nerve are two in number, jugular
and cervical.
The Jugular or Superior Ganglion (ganglion of the root) is situated
within the posterior lacerated foramen. It is grayish in color, oval or
nearly spherical in shape, about two lines in diameter, and embraces all
the fibres of the nerve. It has branches communicating with the facial
nerve while the latter is in the aqueductus Fallopii, and with filaments
from the glosso-pharyngeal nerve and from the nerve of Arnold—with
the petrous ganglion of the glosso-pharyngeal, the spinal accessory
nerve, and the sympathetic system.
The Cervicol or Inferior Ganglion (ganglion of the trunk or ])lexiform
ganglion) is situated upon the pneumogastric nerve a little below the
base of the skull, a half inch beneath the superior ganglion. It is of a
reddish-gray color, loose or plexiform in texture, and contains gray
fibres and nerve-cells interspersed between its white fi!)rcs. It is flat-
tened and cylindrical in shape, and measures from six to ten lines in
length and two lines in width. Its communication with other nerves is
complicated, all of its fibres not passing through to become involved in
their functions. Its branches of communication are
1. The Accessory Portion of the Hpinal Accessory.—This is the most