The glosso-pharyngeal or ninth cranial nerves are mixed nerves and each is attached to the medulla by several roots which enter the posterolateral sulcus, dorsal to the anterior end of the olivary body and in direct line with the facial nerve.
The filaments, when traced lateralward, are seen to blend, in front of the flocculus, into a trunlc which hes in front of the vagus nerve, but which passes through a separate opening through the arachnoid and the dura mater and through the jugular foramen. In the foramen this trunk hes in front, and lateral to the vagus nerve in a groove on the petrous portion of the temporal bone; and in this situation two ganglia are interposed in it, a superior or jugular, and an inferior or petrosal. After it emerges from the jugular foramen the glosso-pharyngeal nerve descends at first between the internal carotid artery and the internal jugular vein and to the lateral side of the vagus; then, bending forward and medialward, it descends medial to the styloid process and the muscles arising from it, and turning around the lower border of the stylo-pharyngeus it passes between the internal and the external carotid arteries, crosses the superficial surface of the stylo-pharyngeus, and runs forward and upward medial to the hyoglossus muscle and across the middle constrictor and the stylo-hyoid ligament, to the base of the tongue.
The superior or jugular ganglion (ganglion of Ehrenritter), is a small, ovoid, reddish-grey body which lies on the back part of the nerve-trunk in the upper part of the jugular foramen. No branches arise from it. It is sometimes continuous with the petrosal ganglion or it may be absent.
The inferior or petrosal ganglion, (ganglion of Andersch), is an ovoid grey body which lies in the lower part of the jugular foramen, and appears to include all the fibers of the nerve.
Branches and communications
- The petrosal ganglion is connected with the superior cervical ganglion of the sympathetic by a fine filament.
- It also has a filament of communication with the auricular branch of the vagus which varies inversely in size with the latter branch and sometimes entirely replaces it. This filament may be absent.
- An inconstant communication with the ganglion of the root of the vagus.
- A short distance below the petrous gangUon the trunk of the nerve is connected by a twig with that branch of the facial nerve which supplies the posterior belly of the digastric muscle. There is also a small twig (probalily sensdryl to the stylo-hyoid.
- From the petrosal ganglion : The tympanic branch (nerve of Jacobson) arises from the petrosal ganglion and passes through a foramen, which lies in the ridge of bone between the carotid canal and the jugular fossa, into the tympanic canahculus (Jacobson's canal), where it is surrounded by a small, fusiform mass of vascular tissue, the iniumesceniia tympanica. After traversing the tympanic canaliculus it enters the tympanum at the junction of its lower and medial walls, and, ascending on the medial wall, breaks up into a number of branches which take part in the formation of the tympanic plexus on the surface of the promontory. The continuation of the nerve emerges from this plexus as the small superficial petrosal nerve, which runs through a small canal in the petrous portion of the temporal bone, beneath the canal for the tensor tympani, and appears in the middle fossa of the cranium through a foramen which lies in front of the hiatus Fallopii. From this foramen it runs forward and passes through the foramen ovale, the canaliculus innominatus, or the spheno-petrosal suture, and enters the zygomatic fossa, where it joins the otic ganghon. While it is in tlie canal in the temporal bone the small superficial petrosal nerve is joined by a geniculo-tympanic branch from the geniculate gangUon of the glosso-palatine nerve.
- Branches from the tympanic plexus :
- The tubal branch (ramus tubae), a delicate branch, which runs forward to the mucous membrane of the tuba auditiva (Eustachian tube) and sends filaments backward to the region of the fenestra vestibuli (ovahs) and the fenestra cochlear (rotunda).
- The superior and inferior carotico-tympanic (carotid) branches pass medianward to the internal carotid plexus.
The above communications carry fibers almost entirely concerned with the sympathetic plexuses of the head and they will be again mentioned below with the gangUated cephalic plexus.
Branches from the trunk of the nerve :
- Pharyngeal branches, which may be two or three in number, arise from the nerve a short distance below the petrosal ganglion. The principal and most constant of these passes on the lateral side of the internal carotid artery, and after a very short independent course joins with the pharyngeal branch of the vagus and with branches of the superior cervical ganglion to form the pharyngeal plexus.
- A muscular brancli is distributed to the stylo-pharyngeus muscle. This branch receives a communication from the facial nerve.
- The tonsillar branches are a number of small twigs which arise under cover of the hyo-glossus muscle; they proceed to the tonsil, around which they form a plexus, the circulus tonsillaris. From this plexus fine twigs proceed to the glosso-palatine arches (pillars of the fauces) and to the soft palate.
- The lingual branches are the terminal branches of the nerve and supply the mucous membrane of the posterior half of the dorsum of the tongue, where, chiefly as taste-fibers, they are distributed to the vallate papillae. Some small twigs pass backward to the follicular glands of the tongue, and to the anterior surface of the epiglottis. Other twigs are distributed around the foramen officum, where they communicate with the corresponding twigs of the opposite side.
The sensory fibers
The sensory fibers of the glosso-pharyngeal nerve spring from the superior and petrosal ganglia and pass peripherally and centrally. The peripheral processes of the ganglion cells are those which are distributed to the mucous membrane (taste-buds) of the tongue and pharynx, and the central processes pass medialward to the medulla. In the medulla they pass dorsalward and medianward through the reticular formation and, bifurcating into ascending and descending branches, they end in the nucleus of termination of the glosso-pharyngeal nerve, that is, in the superior part of the nucleus alae cinereae and in the nucleus of the tractus solitarius.
The motor fibers arise from the nucleus ambiguus in the lateral funiculus of the medulla, in fine with the nucleus of origin of the facial nerve. From this nucleus they pass at first dorsalward and then, turning lateralward, they emerge and join the sensory fibers and run with them in the trunk of the nerve.
Van Gehuchten's observations point to the conclusion that one motor nucleus of the glosso-pharyngeal nerve is separate from and Kes above and to the medial side of the nucleus ambiguus, and that a portion of the nucleus of the ala cinerea is also a motor nucleus common to the glosso-pharyngeal and vagus nerves. It is quite probable that the former motor nucleus is that now considered as the dorsal motor nucleus of the vagus. An unknown proportion of the motor fibers are visceral motor and course in the various communications of the glosso-pharyngeal nerve with cephalic plexus.
The nuclei of termination of the glosso-pharyngeal nerve are associated with the motor nuclei of other cranial nerves by the medial longitudinal fasciculus, and with the somaesthetic area of the cortex cerebri of the opposite side by the medial lemniscus (fillet). The motor nucleus of the nerve is associated with the somaesthetic area by the pyramidal fibers.