Page 300 - My FlipBook

310 ANATOMY.

which form a series of arches beneath the platysma rayoides muscle,
extending inward to the suprahyoid region. It supplies the platysma
myoides and the skin in this region, and communicates with the super-
ficial cervical plexus.
Auditory Nerve.

The Auditory or Eighth Nerve (portio mollis of the seventh nerve,
according to Willis) is the special nerve of hearing, and is distributed to
the ear alone. It arises superficially or apparently by two roots, which
are situated between the olivary and restiform bodies just posterior,
though closely in apposition, to the facial or seventh nerve. On leav-
ing the medulla oblongata the two roots unite, and the nerve then
passes, together with the facial, to the bottom of the internal auditory
meatus. Here it terminates by separating into superior and inferior
divisions.
The tinperior Division breaks up into three branches, which pass to
the utricle, and ampullae of the superior and external semicircular
canals of the ear.
The Inferior Division is chiefly distributed to the cochlea, though it
also supplies the saccule and posterior semicircular canal.
The Nerve of Wrisberg is situated between the auditory and facial
nerves from their origin to the termination of the auditory nerve.
Some of its fibres unite with those of the auditory nerve, while the
nerve itself is connected with the geniculate ganglion of the facial nerve.

Glosso-pharyngbal Nerve.
The Glosso-phari/ngeal or Ni)ifh iVerve (the first and smallest trunk
of the eighth pair, according to Willis) (Fig. 150) is the sensory nerve
of the mucous membrane of the pharynx, the posterior third of the
tongue, and the middle ear. It is also the nerve which controls the
motions of the stylo-pharyngeal muscle. It communicates through
the otic ganglion with the inferior maxillary division of the fifth
nerve, the facial and pneumogastric nerves, and the sympathetic sys-
tem. Its superficial or apparent origin is from the upper or anterior
surface of the medulla oblongata, in the groove between the olivary and
restiform bodies, and between the ])nQumogastric and auditory nerves.
It arises by four or five filaments, which are collected into two bundles,
the anterior being the larger. It passes from its origin outward and
forward beneath the anterior portion of the flocculus, and makes its
exit from the brain-case through the middle compartment of the pos-
terior lacerated foramen in company with the pneumogastric and spinal
accessory nerves. It has a se})arate sheath of its own, however, formed
from the dura mater. Within the foramen the nerve assumes the form of
a slender rounded cord, and ]iasses through in a groove which is occasion-
ally transformed into a canal, the most anterior of the three nerves. While
in this groove or canal tlie nerve is characterized by two enlargements, the
superficial lieing the jugular, and the inferior the petrous ganglion. From
the posterior lacerated foramen the nerve passes forward between the inter-