The =glosso-pharyngeal nerve= (N. glossopharyngeus) is attached to the
anterior part of the lateral aspect of the medulla by several filaments
(Fig. 499). The root-bundles enter the furrow ventral to the restiform
body; they are separated by a short interval from the origin of the
facial nerve, but are not marked off behind from the roots of the vagus.
The bundles converge laterally to form a nerve which perforates the dura
mater and emerges through the foramen lacerum posterius just in front of
the tenth nerve (Fig. 515). As it issues from the cranium the nerve
bears a considerable ovoid gray enlargement, the =petrous ganglion= (G.
petrosum).[204] It then curves downward and forward over the guttural
pouch and behind the great cornu of the hyoid bone, crosses the deep
face of the external carotid artery, and divides into pharyngeal and
lingual branches (Fig. 437). The collateral branches are as follows:
1. The =tympanic nerve= (N. tympanicus) (Fig. 515) arises from the
petrous ganglion and passes upward between the petrous and tympanic
parts of the temporal bone to reach the cavity of the tympanum. Here it
breaks up into branches to form, along with branches from the carotid
plexus of the sympathetic, the =tympanic plexus=. From the plexus
branches pass to the mucous membrane of the tympanum and the Eustachian
tube. The continuation of the nerve issues from the plexus and unites
with a filament from the geniculate ganglion of the facial to form the
small superficial petrosal nerve; this runs forward and ends in the otic
ganglion.
Filaments also connect the petrous ganglion with the jugular ganglion
of the vagus nerve and with the superior cervical ganglion of the
sympathetic.
2. A considerable branch runs backward on the guttural pouch,
contributes filaments to the pharyngeal plexus, and concurs with twigs
from the vagus and the sympathetic in forming the carotid plexus on the
terminal part of the carotid artery and on its chief branches. In this
plexus is the small ganglion intercaroticum.
The =pharyngeal branch= (R. pharyngeus) (Fig. 437) is the smaller of the
two terminal branches. It runs forward across the deep face of the great
cornu of the hyoid bone and concurs with the pharyngeal branches of the
vagus and with sympathetic filaments in forming the pharyngeal plexus;
from this branches pass to the muscles and mucous membrane of the
pharynx.
The =lingual branch= (R. lingualis) is the continuation of the trunk
(Fig. 437). It runs along the posterior border of the great cornu of the
hyoid bone in front of the external maxillary artery and dips under the
hyo-glossus muscle. It gives collateral branches to the soft palate,
isthmus faucium, and tonsil, and ends in the mucous membrane of the
posterior part of the tongue, where it supplies gustatory fibers to the
vallate papillæ. A considerable branch unites with a twig from the
lingual nerve.
The glosso-pharyngeal is a mixed nerve, containing both motor and
sensory fibers. The latter constitute the bulk of the nerve and
include those which mediate the special sense of taste. They are
processes of the cells of the petrous ganglion. The central processes
of the ganglion cells enter the medulla, pass upward and inward
through the formatio reticularis, and end in the nucleus of
termination in the floor of the fourth ventricle. The motor fibers
arise from dorsal and ventral efferent nuclei in the medulla. The
glosso-pharyngeal shares these nuclei with the vagus and has
practically the same central connections as that nerve (_q. v._).