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The Trochlearis or fourth, the smallest cranial nerve, | medulla, and leave the cranial cavity through the jugular lies at the outer side of the crus cerebri. When traced foramen. This nerve, purely motor in function, is subbackwards to its origin it is seen to sink into the valve of divided into two parts, an internal and an external. The Vieussens, where its fibres divide into three roots : one external passes obliquely outwards across the side of the decussates across the valve with a root of the corresponding neck, pierces the sterno-mastoid, and ends in the trapezius, nerve on the opposite side; another passes backwards to both of which muscles it supplies. The internal joins the the locus cæruleus; the third sinks into the corpora quadri- pneumogastric nerve, of which it forms the motor or accesgemina and reaches the Sylvian group of nerve cells, from sory root, and is distributed along with it. which the third nerve also arises. The fourth nerve runs The Hypoglossal or ninth nerve springs out of the groove forward in the outer wall of the cavernous sinus, enters between the anterior pyramid and olivary body of the the orbit through the sphenoidal fissure, and ends in the medulla oblongata, in series with the anterior roots of the superior oblique muscle. It also communicates with the spinal nerves. Its roots pass through the medulla to the cavernous plexus of the sympathetic.
floor of the fourth ventricle, to arise from the nerve cells The Abducent or sixth nerve springs out of the groove in two nuclei of grey matter situated close to the median between the lower border of the pons and the anterior furrow. This grey matter is in series with the anterior pyramid of the medulla oblongata. Its roots sink deeply cornua in the spinal cord. The nerve passes out of the into the pons, and arise from a nucleus of grey matter at skull through the anterior condyloid foramen, and arches the floor of the fourth ventricle, common to it and the portio across the side of the neck to the tongue, to end in glossal. dura. The sixth nerve runs forward in the inner wall of branches for the supply of the intrinsic and extrinsic the cavernous sinus, enters the orbit through the sphenoidal muscles of the tongue. It also gives off--a, the descendens fissure, and ends in the external rectus muscle. It com- noni branch, which, after been joined by the communicantes municates with the carotid plexus of the sympathetic. noni from the cervical plexus, supplies the omo-hyoid,
The Portio dura or motor facial portion of the seventh sterno-hyoid, and sterno-thyroid inuscles ; 6, the thyro-hyoid nerve springs out of the groove between the lower border branch to the thyro-hyoid muscle ; c, the genio-hyoid of the pons and the restiform body. Its roots sink deeply branch to the genio-hyoid muscle. It communicates in the into the pons, and whilst some of its fibres arise from a neck with the sympathetic, vagus, lingual branch of the grey nucleus, at the floor of the fourth ventricle, common fifth, and cervical plexus. to it and the sixth nerve, others ascend from a nucleus The group of mixed nerves will now be considered. which, according to Meynert, lies just on the outer side of The Trifacial or fifth is the largest cranial nerve. It Mixed the superior olivary body, and others again decussate springs by two distinct roots out of the side of the pons.
cranial across the median raphe of the pons. An accessory por- The smaller or motor root arises from the nerve cells of a tion, called portio intermedia, which is said to arise from nucleus of grey matter situated in the back of the pons, the lateral columns of the cord, joins the portio dura. near the floor of the upper part of the fourth ventricle. The portio dura enters the internal auditory meatus in the The larger or sensory root has, according to Meynert, a petrous-temporal bone along with the auditory nerve; but complex origin—a, from a nucleus of grey matter in the at the bottom of the meatus it leaves that nerve and enters pons to the outer side of the origin of the motor root; b, the aqueduct of Fallopius along which it is conducted by descending fibres which arise from nerve cells in the through the bone to emerge at the stylo-mastoid foramen. substance of the corpora quadrigemina, from the grey When in the aqueduct it forms a knee-shaped bend, and matter of the locus cæruleus, and from the longitudinal expands into a small ganglion, which is joined by the fibres of the pons ; c, by ascending fibres which apparently great, small, and external petrosal nerves, and through the arise from the grey tubercle of Rolando ; d, probably by external petrosal it communicates with the sympathetic. fibres which traverse and embrace the superior peduncle of The portio dura gives off—a, a minute branch to the sta- the cerebellum. As the large sensory root of the fifth lies pedius muscle ; b, the chorda tympani, which, entering the on the petrous bone it expands into the Gasserian ganglion, tympanum, passes across that cavity, emerges through the which resembles in structure the ganglion on the posterior Glaserian fissure, and joins the lingual branch of the fifth root of a spinal nerve. From this ganglion three large nerve, which it accompanies as far as the submaxillary branches arise, named respectively the 1st, 2d, and 3d ganglion; it gives a branch to the ganglion, and one to divisions of the ganglion. the lingualis muscle. After the portio dura has passed The 1st or Ophthalmic division is the upper sensory nerve through the stylo-mastoid foramen it gives of --C, the poste of the face, and divides into three branches, which pass rior auricular branch to the occipital belly of the occipito- out of the cranial cavity through the sphenoidal fissure. By frontalis and to the retrahens aurem muscle, and d, the its lachrymal branch it supplies the lachrymal gland, and digastric branch to the posterior belly of the digastric and the outer part of the skin and conjunctiva of the upper eyestylo-hyoid muscles; and then runs forwards through the lid ; by its frontal branch, the inner part of the skin and parotid gland to the face, where it breaks up into numerous conjunctiva of the upper lid, and the skin of the forehead; (e) facial branches to supply the facial muscles of expres- by its oculo-nasal branch, it gives long ciliary nerves to the sion and the buccinator muscle. The facial is also the eyeball, and a nasal nerve to the mucous membrane of secretory nerve for the salivary glands. Through the the nose, and the skin of the side of the nose. From the chorda tympani it influences the secretion of the submaxil- oculo-nasal nerve arises the long or sensory root of the lary and sublingual glands, and through the connection ciliary ganglion, which lies in the cavity of the orbit, and between its lesser petrosal nerve and the auriculo-temporal which receives also a motor root from the third nerve, and in the otic ganglion it influences the parotid gland. a root from the sympathetic. This ganglion gives origin to
The Spinal Accessory is the lowest division of the eighth the short ciliary nerves for the eyeball. nerve. It springs out of the side of the medulla oblongata, The 2d or Superior Maxillary division is the sensory and from the lateral column of the cervical part of the nerve for the middle part of the face. It leaves the sku!] spinal cord as low as the fifth cervical nerve : its roots by the foramen rotundum, passes across the spheno-maxillar y arise from the intermedio-lateral group of nerve cells in fissure, then lies in the canal in the floor of the orbit, froii the cord, and from a nucleus of grey matter in the floor of which it emerges on the face through the infra-orbit-ul the fourth ventricle. The spinal fibres of origin enter the foramen as the infra-orbital nerve. It gives off a small skull through the foramen magum, join the fibres from the orbital branch to a small part of the skin of the temple
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and that over the cheek bone; dental branches to the teeth the temple, forehead, and face, freely communicate with in the upper jaw; palpebral branches to the skin and con the branches of the portio dura, which supply the muscles junctiva of the lower eye-lid; nasal branches to the skin situated in those regions. and mucous membrane of the nose; labial branches to the The Glosso-pharyngeal or uppermost division of the eighth skin and mucous membrane of the upper lip. It also nerve springs out of the side of the medulla oblongata gives off, when in the spheno-maxillary fossa, spheno- between the olivary and restiform bodies; its roots arise palatine branches, which form the sensory root of the from two small masses or nuclei of grey matter in the floor spheno-palatine or Meckels ganglion. This ganglion receives of the 4th ventricle. The nerve passes out of the skull a motor root through the great petrosal nerve from the through the jugular foramen, where it possesses two small knee-shaped bend of the portio dura, and a sympathetic ganglia, named jugular and petrous.
It then passes root from the carotid plexus, which runs along with the across the side of the neck and gives off carotid branches, great petrosal, and forms with it the vidian nerve. The which run along the internal carotid artery; pharyngeal ganglion gives origin to—a, an orbital branch, which supplies branches to the mucous membrane of the pharynx ; tonsila layer of non-striped muscular fibres, described by H. itic branches to the tousil and soft palate; glossal Müller and Turner as developed in connection with the branches to the base of the tongue and the circumvallate periosteum of the orbit, where it covers the spheno-maxillary papillæ, which branches are unquestionably nerves of the fissure ; 6, upper nasal and naso-palatine branches to the special sense of taste; muscular branches to the stylomucous membrane of the nose and hard palate ; c, descend-pharyngeus and perhaps the constrictor muscles. Through ing palatine branches to the mucous membrane of the hard the jugular and petrous ganglia the nerve communicates and soft palate; d, pterygo-palatine to the mucous mem- with the vagus and sympathetic. The petrous ganglion brane of the upper part of the pharnyx.
gives off the tympanic branch or nerve of Jacobson, which The 3d or Inferior Maxillary division passes out of the enters the tympanic cavity, supplies its mucous membrane, skull through the foramen ovale, and as it does so is joined and gives off three communicating branches—one to the by the motor root of the 5th. By the junction a mixed sympathetic; a second to the great petrosal, and through it nerve is formed, which is the sensory nerve for the lower to the knee-shaped bend of the facial; a third to the small part of the face, and the skin of the temple, and the motor petrosal, and through it to the otic ganglion. nerve for the muscles of mastication. Immediately after The Pneumogastric or Vagus is the middle subdivision passing through the foramen this nerve divides into a of the eighth cranial nerve. It springs out of the side of the small and large division, in each of which motor and medulla oblongata, between the olivary and restiform sensory
fibres are found. The small division supplies motor bodies; its roots arise from a nucleus of grey matter in masticatory branches to the masseter, temporal, external, the floor of the 4th ventricle, which nucleus, along with and internal pterygoid muscles; but further it gives off a those for the glosso-pharyngeal nerve, is in series with the long buccal branch, which, though often described as the posterior cornu of grey matter in the spinal cord. It goes motor nerve for the buccinator muscle, is really a sensory through the jugular foramen, is joined by the inner divinerve for the skin and mucous membrane of the cheek. sion of the spinal accessory which is its motor root, then The sensory nature of this nerve is proved, not only by passes down the side of the neck, enters the thorax, reaches physiological and pathological experiments, but by tracing the outer wall of the wesophagus, accompanies that tube its fibres through the buccinator muscle to the mucous through the diaphragm, and terminates in the wall of the membrane. Turner has also recorded two cases in which stomach. The left nerve lies on a plane anterior to the the long buccal nerve arose as a branch of the sensory right: it crosses in front of the arch of the aorta, and is dissuperior maxillary nerve. The large division separates tributed to the anterior wall of the stomach, whilst the right into three branches-a, auriculo-temporal, which ascends to nerve supplies the posterior wall. Each nerve possesses supply the parotid gland, the skin of the auricle, external high in the neck two enlargements, named upper and lower meatus, and temple, and the temporo-maxillary joint; b, in- ganglia. The branches of the vagus are numerous and imferior dental, which enters the dental canal in the lower jaw, portant. The upper ganglion gives origin to the auricular and supplies the lower set of teeth and the skin and mucous branch, which traversing a small canal in the petrous tempomembrane of the lower lip; it also gives off a mylo-hyoid ral bone, is distributed to the skin of the back of the auricle. branch to the mylo-byoid and anterior belly of the digas- The lower ganglion gives origin to—a, the pharyngeal tric muscle; c, lingual or gustatory, which runs forward branch, which forms a plexus with the glosso-pharyngeal along the side of the tongue to end in the filiform and and sympathetic nerves, from which the muscles of the fungiform papillæ of its mucous membrane. The lingua! pharynx are supplied ; 6, the superior laryngeal, which branches are sensory nerves of touch, though some physiolo- divides into an external branch to supply the crico-thyroid gists believe that they are also nerves of taste. Connected muscle, and an internal, which pierces the thyro-hyoid memwith the branches of the inferior maxillary division are brane, and supplies the mucous lining of the larynx and the two small ganglia, which, like the ciliary and spheno-pala- mucous covering of the epiglottis. The trunk of the nerve tine ganglia, are of a greyish colour, contain nerve cells, gives origin to-a, the recurrent laryngeal branch, which on and receive roots from motor, sensory, and sympathetic the right side turns round the subclavian artery, and on the nerves. The submaxillary ganglion lies under cover of the left round the arch of the aorta, and ascends to the larynx to mylo-hyoid muscle, and receives a root from the motor supply its intrinsic muscles except the crico-thyroid ; 6, chorda tympani nerve, a root from the sensory lingual, and cardiac branches, which arise from the nerve partly in the a sympathetic root. It gives branches to the sub-maxillary neck and partly in the chest, and join the great cardiac and sublingual salivary glands. The otic ganglion lies close plexus for the heart ; c, pulmonary branches, which arise to the Eustachian tube, and receives a root from the mus in the chest, pass into the substance of the lungs, and form cular nerve to the internal pterygoid, a root from the along with the sympathetic an anterior plexus in front of, sensory auriculo-temporal, and a sympathetic root. It also and a posterior plexus behind the root of the lung; d, receives the small petrosal nerve, by which it is connected oesophageal branches, which supply the coats of the to the knee-shaped bend of the portio dura and to the wesophagus; e, gastric branches, which supply the coats glosso-pharyngeal nerve. It supplies the tensor tympani of the stomach, and give important offshoots to the great and tensor palati muscles. The branches of the three divi- solar plexus of the sympathetic situated at the pit of the sions of the fifth cranial nerve, which pass to the skin of stomach.
DESCRIPTIVE ANATOMY OF THE SYMPATHETIC NERVOUS
pulinonary plexus. d, Vaso-motor branches or nervi molles,
which supply the muscular coat of the arteries : those which SYSTEM.
arise from the cranial prolongation of the superior cervical Sympathe The Sympathetic Nervous System consists of a pair of ganglion supply the internal carotid artery and its branches fic nervous gangliated cords, situated one on each side of the spinal to the brain and eyeball : those which arise from the ystem.
column; of three great gangliated prevertebral plexuses superior cervical ganglia itself supply the external carotid
meningeal artery the otic ganglion derives its sympathetic Gangliated Each Gangliated Cord of the sympathetic extends along root : the vaso-motor nerves which arise from the middle ord and the side of the spine from the base of the skull to the cervical ganglion supply the inferior thyroid artery, and pass branches.
coccyx. In the neck it lies in front of the transverse to the thyroid gland: the vaso-motor branches of the inferior
9, Hypogastric branches, from the lumbar and sacral ganglia
at the base of the heart, and is divided into a superficial preverBy the Communicating branches this portion of the part, which lies in the concavity of the arch of the aorta,
plexuses. sympathetic is connected with most of the cranial and and a deep part between the aorta and trachea. It receives with the anterior divisions of all the spinal nerves, so as to the cardiac branches of the pneumogastric and the cervical bring the cerebro-spinal and sympathetic systems into close ganglia of the sympathetic. It contains collections of anatomical and physiological relation with each other. nerve cells and a dense plexiform arrangement of nervo It is important also to observe that each communicating fibros. It gives off branches to the heart, which wind branch contains not only non-medullated nerve fibres from around the surface of that organ and penetrate its muscular the sympathetic system to the cerebro-spinal nerves, but substance : on these branches minute ganglia are found medullated fibres from the cerebro-spinal to the sympa- which regulate its rhythmical movements. Through these thetic, so that a double interchange takes place between branches and the cardiac plexus the heart is brought into the two systems. The cranial prolongation of the sympa- connection with both the cerebro-spinal and sympathetic thetic and the superior cervical ganglion communicate with systems of nerves. The sympathetic apparently regulates the 3d and 4th nerves, the Gasserian ganglion of the 5th, the its contraction, for when this nerve is stimulated the action 6th, the portio dura of the 7th, the glosso-pharyngeal and of the heart is accelerated. The pneumogastric again exerpneumogastric of the 8th, and the 9th cranial nerves, and cises an inhibitory or restraining influence on the contracwith the anterior divisions of the four upper cervical spinal tions of the organ, for when this nerve is irritated the nerves. The middle cervical ganglion communicates with activity of contraction is diminished, but when divided it the 5th and 6th cervical nerves, the inferior cervical gau- is greatly increased. The cardiac plexus also sends offsets glion with the 7th and 8th cervical nerves, the twelve to the anterior and posterior pulmonary plexuses for the thoracic ganglia with the series of intercostal nervez, the supply of nerves to the lungs. five lumbar ganglia with the series of lumbar spinal nerves, The Prevertebral Solar or Epigastric plexus is situated at the sacral and coccygeal ganglia with the sacral nerves and the pit of the stomach around the coeliac axis, a branch of the coccygeal nerve.
the abdominal aorta. It receives the great and small The Distributory branches of the gangliated cord are as splanchnic nerves from the thoracic ganglia of the sympafollows:-a, Pharyngeal branches from the superior cervical thetic, and some of the terminal branches of the pneumoganglion, which join the pharyngeal branches of the glosso- gastric nerve. It contains large collections of nerve cells, pharyngeal and pneumogastric nerves, to form the pharyn- which form the two semilunar ganglia, and a dense plexigeal plexus, which supplies the muscles and mucous form arrangement of nerve fibres. It gives origin, either membrane of the pharynx. b, Articular branches from the directly or indirectly, to numerous plexiform branches, upper thoracic and the lumbar ganglia to the articulations which accompany, and are named after, the abdominal between the adjacent vertebræ. c, Pulmonary branches from aorta and its various branches given off to the walls and the 3d or 4th thoracic ganglia, which join the posterior | viscera of the abdomen proper. In this manner, not only
do the arteries which supply the abdominal viscera receive
ORGANS OF SENSE. their vaso-motor nerves, but the muscular and mucous coats of the stomach, intestines, gall bladder, bile ducts, The organs of sense are the organs through the interme ureters, and seminal ducts, and the glandular structures of diation of which the mind becomes cognisant of the appearthe liver, pancreas, kidneys, spleen, and supra-renal cap- ance and properties of the various objects in the external sules. It is important also to observe that these plexuses world. These organs are severally named nose, eye, ear, of distribution not unfrequently contain small ganglia, tongue, and skin. For the excitation and perception of a and the branches which supply the muscular coat of the sensation three sets of structures are necessary: a, a stomach and intestines have minute microscopic ganglia, peripheral end-organ;, b, a sensory nerve ; c, a central with stellate nerve cells lying amidst them. The distribu
The distribu- organ. The peripheral end-organ is the part of the appation of the pneumogastric nerve to the stomach, and its ratus to which the stimulus necessary for the production of connection with the solar plexus, enables that nerve to the sensation is applied. This stimulus causes nervous stimulate its peristaltic contraction, and, according to some impulses to be propagated from the end-organ along the experimenters, that of the small intestine also; but the fibres of the sensory nerve to the central organ, in which precise action of the sympathetic on these organs is still a that nerve terminates at its central extremity. These nerdisputed question.
vous impulses occasion molecular changes in the nerve cells The Prevertebral Hypogastric plexus is situated in front of the brain, and the mind becomes conscious of a sensation. of the last lumbar vertebra. It receives branches from the The shape and construction of each organ of sense is adapted lumbar ganglia of the sympathetic, and from the plexus to the application of the stimulus required for the producsurrounding the abdominal aorta. It divides into two tion of the particular sensation to which the organ is subparts, which lie one on each side of the rectum, and are servient. Each organ of sense possesses its own charactercalled the pelvic plexuses ; these plexuses are joined by istic form of end-organ. The touch corpuscles of the skin, branches from the sacral ganglia of the sympathetic, and the end bulbs found in several mucous membranes, and the from the 3d and 4th sacral spinal nerves, and contain Pacinian corpuscles, are the end-organs occurring in their small gangliform collections of nerve cells. From the several localities; they have the peripheral ends of the pelvic plexuses numerous plexiform nerves arise, which sensory nerves terminating in their substance, and the accompany the internal iliac artery and its branches to the axial cylinder of the nerve fibre ends in their interior. walls and viscera of the pelvis, and are named after them. The rods and cones of the retina, the rods of Corti in These nerves not only supply the vaso-motor nerves for the cochlea, the olfactory cells of the nose, and the gusthese blood-vessels, but also the muscular coat and mucous tatory bodies in the tongue, are the end-organs belong. membrane of the bladder, rectum, and urethra, besides ing to their several organs of sense; the sensory nerve the prostate gland in the male, and the uterus and vagina, fibres which terminate in relation with them have not and in part the ovary, in the female ; in connection with yet, however, been traced into actual continuity with their distribution to these viscera, minute ganglia are their substance.
their substance. A stimulus, whatever may be its nature, found lying amidst the nerves, the nerve cells in which applied to any organ of sense can excite only that kind of act undoubtedly as centres of reinforcement for the origin sensation for the production of which the organ is subserof additional nerve fibres.
vient. Thus a stimulus applied to the eye, whether it be From the distribution of the branches of the gangliated the natural stimulus of the waves of light, the mechanical cord of the sympathetic, and of the gangliated prevertebral stimulus of a blow, or an electric stimulus, can only excite plexuses, it will be seen that this nerve is especially related the sensation of light. Stimuli applied to the ear can only to the blood vessels and to the viscera contained within excite the sensation of sound, and in like manner with the the great cavities of the body. As the cerebro-spinal sys- other senses. In studying the anatomy of the organs of tem is engaged in the supply of nerves to the voluntary sense the arrangement of numerous accessory structures, muscles, the sympathetic is the medium of supply for the which assist either in conducting stimuli or in modifiying involuntary muscular apparatus, both in the coats of the their effects, the arrangement and structure of the peripheral vessels and in the walls of the hollow viscera. But end-organs, and the origin, course, and distribution of the though the vaso-motor nerves branch from the sympathetic sensory nerves, will have to be considered. ganglia, it must not be supposed that they have no connection with the cerebro-spinal system. The communicat The Nose or organ of smell is a large cavity situated in Nose. ing branches between the sympathetic ganglia and the the face, between the orbits, above the mouth, and below anterior divisions of the spinal nerves establish a connection the cribriform plate of the ethmoid bone. It communicates between them and the cerebro-spinal nervous axis. By by the anterior nares, or nostrils, with the external atmorecent experiments, the tract of transmission of the vaso- sphere, by the posterior nares with the pharynx, and through motor fibres has been traced along with the anterior roots | it with the larynx, trachea, and lungs. It is the proper of the spinal nerves, through the lateral columns of the entrance to the respiratory passage, is accessory to the procord to the medulla oblongata, in which the vaso-motor duction of the voice, aids in the sense of taste, and forms nerve centre lies a little to one side of the mesial plane, one of the most important features of the face. It is subabove the calamus scriptorius. In the distribution of the divided into a right and a left chamber by a vertical mesial sympathetic to the glandular viscera, not only is it im partition, the septum nasi, so that the nose is a double portant to attend to their terminations in the muscular organ in the same sense as the eyes or ears are double. coat of the blood-vessels of the glands, but the termina The walls of the cavity of the nose are formed partiy of tion of the nerves in connection with the secreting cells bone and partly of cartilage. The osseous walls are referred themselves must be taken into consideration. The com to on page 826. The cartilages form the point, the alæ, and munications between the cerebro-spinal and sympathetic a part of the septum nasi. The mesial or septal cartilage is systems, not only through the spinal nerves, but also triangular in shape, and fats into the interval between the through the pneumogastric, are to be kept in mind in con vomer, the mesial plate of the ethmoid, and the nasal spine nection with the effects produced by varying mental con of the superior maxilla. Anteriorly and inferiorly its border ditions on the secretions of the glands.
is free, projects on to the face, and forms the columna of the nose.
The lateral cartilages form the tip and alm. On each side is an upper lateral cartilage attached by its