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Branches and Communications.-(i.) In the internal acoustic meatus the nervus intermedius, lying between the facial and acoustic nerves, sends communicating branches to both of them. The branch to the acoustic nerve probably separates from it again to join the genicular ganglion of the facial nerve.
(ii.) In the canalis facialis the ganglion geniculi is formed at the point where the facial nerve bends backwards. It is an oval swelling on the nerve, and is joined by a branch from the upper (vestibular) trunk of the acoustic nerve, by which it probably receives fibres of the nervus intermedius. From the ganglion three small nerves arise :-(1) The greater superficial petrosal nerve passes forwards through the hiatus canalis facialis to the middle fossa of the skull. In the upper part of the foramen lacerum it is joined by the deep petrosal nerve from the sympathetic plexus on the internal carotid artery to form the nerve of the pterygoid canal, which, after traversing the pterygoid canal, ends in the spheno-palatine ganglion. (2) A minute nerve (ramus anastomoticus cum plexu tympanico) pierces the temporal bone and joins the tympanic branch of the glosso
FIG. 656. THE CONNEXIONS OF THE FACIAL NERVE IN THE TEMPORAL BONE.
pharyngeal in the substance of the bone. By their union the lesser superficial petrosal nerve is formed, which pierces the temporal bone and ends in the otic ganglion. (3) The external superficial petrosal nerve is a minute inconstant branch which joins the sympathetic plexus on the middle meningeal artery.
In the course of the facial nerve in the lower part of the canalis facialis, behind the tympanum, three branches arise-(1) N. Stapedius.-The small nerve to the stapedius muscle, which passes forwards to the tympanum. (2) Chorda Tympani. The chorda tympani nerve (probably associated with the nervus intermedius), which enters the tympanic cavity through the tympanic aperture of the canaliculus chorda, passes over the membrana tympani and the handle of the malleus, and leaves the cavity through the medial end of the petro-tympanic fissure to reach the infra-temporal fossa. Medial to the external pterygoid muscle it becomes incorporated with the lingual branch of the mandibular nerve, and in its further course is inseparable from that nerve. It supplies a root to the submaxillary ganglion, and is finally distributed to the side and dorsum of the tongue in its anterior two-thirds. The chorda tympani nerve receives, under cover of the external pterygoid muscle, a fine communication from the otic ganglion. (3) Before it leaves the canalis facialis a fine communicating branch arises from the facial nerve to join the auricular branch of the vagus nerve.
(iii.) In the neck the facial nerve gives off three muscular branches: (1) and (2)
the Ramus Stylohyoideus, Ramus Digastricus. Small branches supply the stylo-hyoid and the posterior belly of the digastric, the latter nerve sometimes communicating with the glossopharyngeal. (3) N. Auricularis Posterior.-The posterior auricular nerve bends backwards and upwards over the anterior border of the mastoid process along with the posterior auricular artery. It divides into two branches-an Tauricular branch for the posterior auricular muscle and the intrinsic muscles of the auricle, and an occipital branch for the occipital belly of the epicranius muscle.
FIG. 657.-THE DISTRIBUTION OF THE TRIGEMINAL AND FACIAL NERVES ON THE FACE.
The posterior auricular nerve, in its course, communicates with the great auricular, lesser occipital, and auricular branch of the vagus nerves.
(iv.) In the parotid gland the facial nerve spreads out in an irregular series of branches (plexus parotideus), indefinitely divided into a temporo-facial and a cervicofacial division. Communications occur in the substance of the gland between the main trunks and the great auricular and auriculo-temporal nerves.
The temporo-facial division gives off two series of subordinate branches which radiate forwards and upwards from the parotid gland.
1. Rami Temporales.-The temporal branches are of large size, and, sweeping out of the parotid gland over the zygomatic arch, are distributed to the orbicularis oculi, frontalis, corrugator supercilii, auriculares anterior and superior. The temporal branches communicate in their course with the auriculo-temporal, zygomaticotemporal, lacrimal, and supra-orbital branches of the trigeminal nerve.
2. Rami Zygomatici.-The upper zygomatic branches are small, and sometimes are inseparable from the temporal or lower zygomatic nerves. Extending forwards
across the zygomatic bone, they supply the orbicularis oculi and zygomatic muscle, and communicate with the zygomatico-facial branch of the maxillary nerve.
The lower zygomatic branches are of considerable size. Passing forwards over the masseter muscle in company with the parotid duct, they supply the orbicularis oculi, the zygomaticus, buccinator, and the muscles of the nose and upper lip. The infra-orbital plexus is formed by the union of these nerves with the infra-orbital branch of the maxillary nerve below the lower eyelid. Smaller communications occur with the infra-trochlear and nasal nerves on the side of the nose.
The cervico-facial division of the facial nerve supplies three series of secondary branches.
1. Rami Buccales. The buccal branch (or branches) extends forwards to the angle of the mouth to supply the muscles converging to the mouth, including the buccinator. It communicates with the buccinator branch of the mandibular nerve in front of the anterior border of the masseter muscle.
2. Ramus Marginalis Mandibulæ.-The marginal branch of the mandible (O.T. supramandibular) passes along the mandible to the interval between the lower lip and chin, and supplies the triangularis oris, quadratus labii inferioris, and orbicularis oris. It communicates with the mental branch of the inferior alveolar nerve.
3. Ramus Colli.-The cervical branch (O.T. infra-mandibular) emerges from the parotid gland near its lower end, and sweeps forwards below the angle of the mandible to the front of the neck. It supplies the platysma, and forms loops of communication with the nervus cutaneus colli.
The eighth or acoustic nerve (O.T. auditory) arises from the brain by two roots, medial and lateral. The medial, vestibular root emerges between the olive and the restiform body. The lateral, cochlear root, continuous through the cochlear nucleus with the striæ medullares of the fourth ventricle, winds round the lateral side of the restiform body (for the deep connexions, see p. 604). The two roots unite with one another to form the trunk of the nerve, which is attached to the
FIG. 658.-SCHEME OF THE ORIGIN AND DISTRIBUTION OF THE ACOUSTIC NERVE.
brain on the lateral side of the facial nerve and nervus intermedius, at the lower border of the pons (Fig. 643, p. 768).
The nerve passes laterally through the internal acoustic meatus, lying below the facial nerve and nervus intermedius (Fig. 647, p. 771). In the meatus the trunk separates into two divisions, an upper consisting of vestibular fibres only and a lower which consists mainly of cochlear fibres but contains also some vestibular fibres. The divisions subdivide, and their branches pass through the lamina cribrosa, to supply the several parts of the labyrinth.
The superior division in the internal acoustic meatus usually receives fibres
from the nervus intermedius, and gives off a communicating branch to the genicular ganglion of the facial nerve. It then separates into three terminal branches which pierce the lamina cribrosa. (1) N. Utricularis.-The utricular nerve supplies the macula acustica of the utricle. (2) and (3) Nn. Ampullaris Superior et Lateralis.—The superior and lateral ampullary nerves supply the ampullæ of the superior and lateral semicircular ducts.
The inferior division gives off (1) n. saccularis, a saccular nerve to the macula acustica of the saccule, (2) n. ampullaris inferior, an inferior ampullary nerve to the ampulla of the posterior semicircular duct, and (3) is continued through the lamina cribrosa to the labyrinth as the cochlear nerve, which is distributed through the modiolus and osseous spiral lamina to the organ of Corti in the cochlea.
Both the vestibular and cochlear nerves contain among their fibres collections of nerve cells, forming in each nerve a distinct ganglion-the vestibular ganglion on the vestibular trunk, and the ganglion spirale or spiral ganglion of the cochlea on the cochlear trunk.
Va. G. Ph.
The ninth or glossopharyngeal nerve (Fig. 643, p. 768) arises from the brain by five or six fine fila radicularia (radicles) which emerge from the medulla oblongata, between the posterior and lateral columns, close to the facial nerve above, and in series with the fila of the vagus nerve below (for the Aur deep connexions, see p. 596). The fila combine to form a nerve which passes through the jugular foramen, along with the vagus and accessory nerves, but enveloped in a separate sheath of dura mater (Fig. 647, p. 771). Reaching the neck, the nerve arches downwards and forwards to the interval between the hyoid bone and the mandible. In its course to the side of the pharynx it lies at first between the internal carotid artery and the internal jugular vein, and
then between the internal and external carotid arteries. It sweeps round the stylopharyngeus muscle and the stylo-hyoid ligament, and disappears medial to the hyoglossus muscle, to reach its termination in the tongue.
The branches of the nerve may be classified in three series according to their origin-(i.) in the jugular foramen; (ii.) in the neck; (iii) in relation to the tongue.
In the jugular foramen there are two enlargements upon the trunk of the nerve-the superior and petrous ganglia. The superior ganglion (O.T. jugular) is small, does not implicate the whole width of the nerve, and may be fused with the petrous ganglion, or
G.Ph, Glossopharyngeal nerve; J, Superior, and P, Petrous ganglia; Ty, Tympanic nerve; Ty. Plex., Tympanic plexus; Fa, Root from genicular ganglion of facial nerve; S.S. P, Lesser superficial petrosal nerve to the otic ganglion; S.D. P, Carotico-tympanic nerve; I.C, Internal carotid artery; Va, Vagus nerve ; Aur., Auricular branch of vagus; Sy., Superior cervical sympathetic ganglion; F, Communicating branch to facial nerve; Ph, Pharyngeal branch of vagus; E.C, External carotid artery; Ph.Pl, Pharyngeal plexus; S.Ph, Stylopharyngeus muscle; S. H.L, Stylo-hyoid ligament; H.G, Hyoglossus; S.G, Styloglossus; Ton, Palatine tonsil; S. Pal., Soft palate; G. H.G, Genioglossus; G.H, Genio-hyoid; Hy, Hyoid bone.
even absent altogether. No branches arise from it.
Ganglion Petrosum.-The petrous ganglion is distinct and constant. It is placed upon the nerve at the lower part of its course through the jugular foramen.
Branches and Communications of the Petrous Ganglion.-N. Tympanicus.-The tympanic branch is the most important offset from this ganglion. It passes through a small canal in the bridge of bone between the jugular foramen and the carotid canal to reach the cavity of the tympanum, where it breaks up into branches, to form, along with branches from the carotid plexus of the sympathetic on the internal carotid artery (nn. caroticotympanici superior et inferior, O.T. small deep petrosal), the plexus tympanicus Jacobsoni (tympanic plexus), for the supply of the mucous lining of the tympanum, mastoid cells, and auditory tube (Fig. 656, p. 782). The fibres of the tympanic branch of the glossopharyngeal nerve become reunited to form, by their union with a small nerve from the genicular ganglion of the facial nerve (anastomotic with the tympanic plexus), the lesser superficial petrosal nerve in the substance of the temporal bone. This passes forwards through the temporal bone, and eventually joins the otic ganglion.
Besides forming the tympanic branch, the petrous ganglion of the glossopharyngeal nerve communicates with three other nerves (1) with the superior cervical ganglion of the sympathetic; (2) with the auricular branch of the vagus; and (3) sometimes with the jugular ganglion of the vagus.
In the neck the glossopharyngeal nerve gives off two branches. (1) As it crosses over the stylopharyngeus muscle it supplies the nerve to that muscle (ramus stylopharyngeus), fibres of which pierce the muscle to reach the mucous membrane of the pharynx. (2) Rami Pharyngei.—The pharyngeal branches of the nerve supply the mucous membrane of the pharynx directly after piercing the superior constrictor muscle, and indirectly after joining, along with the pharyngeal offsets from the vagus and the superior cervical ganglion of the sympathetic, in the formation of the pharyngeal plexus.
The terminal branches of the nerve supply the mucous membrane of the tongue and adjacent parts. Rami Tonsillares.-A tonsillar branch forms a plexus to supply the mucous membrane covering the palatine tonsil, the adjacent part of the soft palate, and the palatine arches. Rami Linguales.-Lingual branches supply the mucous membrane of the dorsal third and lateral half of the tongue, extending backwards to the glosso-epiglottic folds and the front of the epiglottis.
The tenth or vagus nerve (O.T. pneumogastric) arises from the brain by numerous fila radicularia attached to the floor of the postero-lateral sulcus of the medulla oblongata, in series with the glossopharyngeal nerve above and the accessory nerve below it (for the deep connexions, see p. 656). The fila of the nerve unite to form a single trunk which emerges into the neck through the jugular foramen.
In the jugular foramen the nerve occupies the same sheath of dura mater as the accessory nerve, it is placed behind the glossopharyngeal nerve, and a small ganglion-the jugular ganglion—is developed upon it.
In the neck the vagus nerve pursues a vertical course in front of the vertebral column. It occupies the carotid sheath, lying between and behind the internal and common carotid arteries and the internal jugular vein. It enters the thorax behind the large veins on the right side, after crossing over the subclavian artery; on the left side, in the interval between the left common carotid and subclavian arteries In the upper part of the neck, immediately below the jugular foramen, a second and larger ganglion-the ganglion nodosum-is developed on the trunk of the nerve.
In the thorax the nerves occupy the superior and posterior mediastinal spaces, and their relations are different on the two sides. (a) In the superior mediastinum the right nerve continues its course alongside the innominate artery and the trachea, and behind the right innominate vein and superior vena cava, to the posterior surface of the root of the lung. The left nerve courses downwards between the left common carotid and subclavian arteries, and behind the left innominate vein and the phrenic nerve. It passes over the aortic arch, and then proceeds to the posterior surface of the root of the left lung. (b) In the posterior mediastinum the vagi nerves are concerned in the formation of two great plexuses the pulmonary and the oesophageal. Behind the root of each lung the nerve breaks up to form