Page:The New International Encyclopædia 1st ed. v. 14.djvu/437

* NERVOUS SYSTEM AND BRAIN. 387 NERVOUS SYSTEM AND BRAIN. triolc. The Gasscrian gangliun lios in a depres- sion iii tlic petrous portion of the temporal bone. From tlu' anterior as]iect of the yanj;lion tliree branelies ari' jriven oil — the o))htlialniie, the su- perior maxillary, and the inferior maxillary. The ophthalniie divides into three branches, the laehrymal. frontal, and nasal, which enter the orbit through the sphenoidal fissure and supply the eyeball, lachrymal gland, mucous membrane of the eye and nose, and the skin of the eyebrow, PLAN OF THE FIFTH CRANIAL NERVK. forehead, and nose. Connected with the ophthalmic branch is a small ganglion called the ophthalmic or ciliarj' ganglion. The superior maxillary is the middle of the branches of the Gasserian ganglion. It crosses the sphenomaxillary fossa, in which it gives off" three branches, the orbital, the spheno-palatine. and the posterior dental. The nerve next enters the infra-orbital canal, where it gives off the anterior dental branch. The nerve then passes to the face through the infra-orbital foramen and terminates in palpebral, nasal, and labial branches. The spheno-palatine or ileekel's ganglion is connected with this branch of the fifth nerve. It sends off four main sets of branches: ascending, to the orbit; descending, to the palate; posterior, to the pharynx; and internal, to the nose. The inferior maxillary is the largest branch of the Gasserian ganglion and receives the entire motor portion of the nerve. .Just beneath the base of the skull the nerve divides into two branches, an anterior branch and a posterior branch. The anterior branch contains nearly all the motor fibres, and. splitting up into mas.seteric, deep temporal, buccal, and pterygoid branches, supplies the nuisdes of ma--tication. The posterior division is mainly sensory and is distributed as three branches — the auriculotemporal, gustatory, and inferior dental. Two small ganglia, the otic or Arnold's, and the submaxillary, are connected with this branch of the tilth nerve. The sixth, or abduccns nerve, is a small motor nerve whose libres are axones of a group of cells situated in the floor of the fourth ventricle. The nerve reaches the under surface of the medulla just behind the pons between the pyramid and the olive. It passes through the sjihenoidal fis- sure, enters the orbit, and is distributed entii-ely to the external rectus muscle. The seventh, or facial nerve, is a motor nerve. Its nucleus of origin consists of a group of cells situated deep in the forniatio reticularis of the upper part of the medvilla. The nerve leaves the surface of the brain just behind the pons between the olive and the re.stiform body, tiius lying to the outer side of the sixth nerve. The nerve passes forward and enters the internal auditory meatus with the si.xtli nerve. At the bottom of the meatus it passes into the Fallopian aqueduct, by means of which it traverses the petrous por- tion of the tem])oral bone, finding exit through the stjdomastoid foramen. It then enters the parotid gland, and just behind the jaw divides into two main branches, the tempero-facial and eervico-facial. During its passage through the temporal bone it is connected with a small gray mass known as the geniculate ganglion. Its branches of distribution are as follows: Within the Fallopian ar|ueduct a tympanic branch to the stapedius muscle, and the corda tympani to the muscle of the tongue (lingualis) ; at its exit from the styloid foramen, the posterior auricular branch to the retrahens aurem and part of the occipito-frontalis. the stylo-hyoid to the muscle of that name, and the digastric to the digastric; on the face, the tempero-facial. dividing into tem- poral branches and malar branches, and the eer- vico-facial, distributed to the muscles of the head and face. The eighth, or auditory nerve, is the nerve of the special sense of hearing and is distributed to the internal ear. The nerve is composed of two divisions, the cochlear division and the vestibular division. The fibres of the cochlear division are axones of bipolar cells in the ganglion of Corti. The peripheral processes of these cells end among the epithelial cells of Corti"s organ within the cochlea. Their central processes enter the me- dulla at the junction of the medulla and pons and terminate in two nuclei known as the ventral and dorsal nuclei of the cochlear nerve. By means of neurones whose cell bodies are situated in these nuclei, auditory im- pressions are carried to higher centres. The neurones of the vestibular division of the nerve have tlicir cell bodies located in Scarpa's ganglion or the ganglion vestibulare. The.se cells are bipolar and their peripheral processes end among- the hair cells of the crista and mascula acustica. Their central processes enter the medulla and pass to two nuclei of termination in which are cells whose axones carry the impulses to higher centres. See also E.R. The ninth, or glosso-pharyngeal nerve, leaves the upper part of the medulla in the groove be- tween the olive and the restiform body. It con- sists of a sensory part and a motor part. The