Page:Encyclopædia Britannica, Ninth Edition, v. 1.djvu/940

Rh 882 ANATOMY [NERVOUS and that 0-veY the cheek bone ; dental branches to the teeth in the upper jaw ; palpebral branches to the skin and con junctiva of the lower eye-lid ; nasal branches to the skin and mucous membrane of the nose ; labial branches to the skin and mucous membrane of the upper lip. It also gives off, when in the spheno-maxillary fossa, spheno- palatine branches, which form the sensory root of the spheno-palatine or Meckel s ganglion. This ganglion receives a motor root through the great petrosal nerve from the knee-shaped bend of the portio dura, and a sympathetic root from the carotid plexus, which runs along with the great petrosal, and forms -with it the vidian nerve. The ganglion gives origin to a, an orbital branch, which supplies a layer of non-striped muscular fibres, described by H. Miiller and Turner as developed in connection with the periosteum of the orbit, where it covers the spheno-maxillary fissure ; b, upper nasal and naso-palatine branches to the mucous membrane of the nose and hard palate ; c, descend ing palatine branches to the mucous membrane of the hard and soft palate; d, pterygo-palatine to the mucous mem brane of the upper part of the pharnyx. The 3d or Inferior Maxillary division passes out of the skull through the foramen ovale, and as it does so is joined by the motor root of the 5th. By the junction a mixed nerve is formed, which is the sensory nerve for the lower part of the face, and the skin of the temple, and the motor nerve for the muscles of mastication. Immediately after passing through the foramen this nerve divides into a small and large division, in each of which motor and sensory fibres are found. The small division supplies motor masticatory branches to the masseter, temporal, external, and internal pterygoid muscles ; but further it gives off a long buccal branch, which, though often described as the motor nerve for the buccinator muscle, is really a sensory nerve for the skin and mucous membrane of the cheek. The sensory nature of this nerve is proved, not only by physiological and pathological experiments, but by tracing its fibres through the buccinator muscle to the mucous membrane. Turner has also recorded two cases in which the long buccal nerve arose as a branch of the sensory superior maxillary nerve. The large division separates into three branches a, auriculo-iemporal, which ascends to supply the parotid gland, the skin of the auricle, external meatus, and temple, and the temporo-maxillary joint ; b, in ferior dental, which enters the dental canal in the lower jaw, and supplies the lower set of teeth and the skin and mucous membrane of the lower lip; it also gives off a mylo-hyoid branch to the mylo-hyoid and anterior belly of the digas tric muscle; c, lingual or gustatory, which runs forward along the side of the tongue to end in the filiform and fungiform papillae of its mucous membrane. The lingual branches are sensory nerves of touch, though some physiolo gists believe that they are also nerves of taste. Connected with the branches of the inferior maxillary division are two small ganglia, which, like the ciliary and spheno-pala tine ganglia, are of a greyish colour, contain nerve cells, and receive roots from motor, sensory, and sympathetic nerves. The subrnaxillary ganglion lies under cover of the mylo-hyoid muscle, and receives a root from the motor chorda tympani nerve, a root from the sensory lingual, and a sympathetic root. It gives branches to the sub-maxillary and sublingual salivary glands. The otic ganglion lies close to the Eustachian tube, and receives a root from the mus cular nerve to the internal pterygoid, a root from the Bensory auriculo- temporal, and a sympathetic root. It also receives the small petrosal nerve, by which it is connected to the knee-shaped bend of the portio dura and to the glosso-pharyngeal nerve. It supplies the tensor tympani and tensor palati muscles. The branches of the three divi sions of the fifth cranial nerve, which cass to the skin of the temple, forehead, and face, freely communicate with the branches of the portio dura, which supply the muscles situated in those regions. The Glosso-pliaryngeal or uppermost division of the eighth nerve springs out of the side of the medulla obloiigata between the olivary and restiform bodies; its roots arise from two small masses or nuclei of grey matter in the floor of the 4th ventricle. The nerve passes out of the skull through the jugular foramen, where it possesses two small ganglia, named jugular and petrous. It then passes across the side of the neck and gives off carotid branches, which run along the internal carotid artery; pharyngeal branches to the mucous membrane of the pharynx ; tonsil- itic branches to the tonsil and soft palate ; glossal branches to the base of the tongue and the circumvallate papillae, which branches are unquestionably nerves of the special sense of taste ; muscular branches to the stylo- pharyngeus and perhaps the constrictor muscles. Through the jugular and petrous ganglia the nerve communicates with the vagus and sympathetic. The petrous ganglion gives off the tympanic branch or nerve of Jacobson, which enters the tympanic cavity, supplies its mucous membrane, and gives off three communicating branches one to the sympathetic ; a second to the great petrosal, and through it to the knee-shaped bend of the facial; a third to the small petrosal, and through it to the otic ganglion. The Pneumogastric or Vagus is the middle subdivision of the eighth cranial nerve. It springs out of the side of the medulla oblongata, between the olivary and restiform bodies ; its roots arise from a nucleus of grey matter in the floor of the 4th ventricle, which nucleus, along with those for the glosso-pharyngeal nerve, is in series with the posterior cornu of grey matter in the spinal cord. It goes through the jugular foramen, is joined by the inner divi sion of the spinal accessory which is its motor root, then passes down the side of the neck, enters the thorax, reaches the outer wall of the oesophagus, accompanies that tube through the diaphragm, and terminates in the wall of the stomach. The left nerve lies on a plane anterior to the right : it crosses in front of the arch of the aorta, and is dis tributed to the anterior wall of the stomach, whilst the right nerve supplies the posterior wall. Each nerve possesses high in the neck two enlargements, named upper and loiver ganglia. The branches of the vagus are numerous and im portant. The upper ganglion gives origin to the auricular branch, which traversing a small canal in the petrous tempo ral bone, is distributed to the skin of the back of the auricle. The lower ganglion gives origin to a, the pharyngeal branch, which forms a plexus with the glosso-pharyngeal and sympathetic nerves, from which the muscles of the pharynx are supplied ; b, the superior laryngeal, which divides into an external branch to supply the crico-thyroid muscle, and an internal, which pierces the thyro-hyoid mem brane, and supplies the mucous lining of the larynx and the mucous covering of the epiglottis. The trunk of the nerve gives origin to a, the recurrent laryngeal branch, which on the right side turns round the subclavian artery, and on the left round the arch of the aorta, and ascends to the larynx to supply its intrinsic muscles except the crico-thyroid ; b, cardiac branches, which arise from the nerve partly in the neck and partly in the chest, and. join the great cardiac plexus for the heart ; c, pulmonary branches, which arise in the chest, pass into the substance of the lungs, and form along with the sympathetic an anterior plexus in front of, and a posterior plexus behind the root of the lung ; d, cesophageal branches, which supply the coats of the oesophagus ; e, gastric, branches, which supply the coats of the stomach, and give important offshoots to the great solar plexus of the sympathetic situated at the pit of tho stomach.