Page:Encyclopædia Britannica, Ninth Edition, v. 19.djvu/53

Rh VEGETABLE.] PHYSIOLOGY 43 ably to the glands of the velum palati. It contains vaso-motor fibres from the sympathetic for the vessels, and is associated with the spheno- palatine ganglion. (C) The inferior maxillary division of the fifth contains sensory branches to (a) the skin Of the cheeks, temples, lower lip, chin, front part of the ear, and external auditory canal ; (b) the mucous membrane of the cheeks, lips, gums, front part of the tongue, the mucous membrane of the tympanum, and the mastoid cells ; (c) the periosteum of the lower jaw and temporal bones ; ((/) the teeth of the lower jaw ; (e) the temporo-maxillary articulation ; and (/) the muscles in the neighbourhood (muscular sensibility). It thus exercises an influence on taste, hearing, and secretion (see NUTRITION). It contains vaso-motor fibres for the blood-vessels. Its motor branch is distributed to the muscles of mastication ; and it is related to two ganglia, the otic and the sub-maxillary. 6. The sixth nerve is motor, and supplies the external rectus muscle of the eyeball only. 7. The facial or seventh nerve is purely motor, and supplies all the muscles of expression. It also contains secretory fibres influencing the action of the salivary glands (see NUTRITION). Some assert that the chorda tympani con tains gustatory fibres, but the question has not been settled. Claude Bernard found that the facial contains vaso-motor fibres. 8. The auditory or eiyhth nerve is the nerve of hearing (see EAR). In addition to purely auditory filaments it contains fibres from the semicircular canals having to do with impressions of movement in space (see pp. 38, 39). 9. The glosso-pharyngeal nerve is sensory to (a) the mucous membrane of the posterior part of the tongue (nerve of taste), the pillars of the fauces, the anterior face of the epiglottis, and the tonsils ; and (b) the mucous membrane of the tympanum, the fenestra ovalis and fenestra rotunda (see EAR), the mastoid cells, and the Eustachian tube along with the fifth. It probably supplies motor fibres to the muscles of the pharynx, but this is doubtful. Vulpian states that it contains vaso-dilator fibres for the vessels of the posterior third of the tongue. 10. The pneumogastric or vagus nerve has many complicated actions. (A) It is sensitive to (a) the mucous membrane of all the respiratory passages, includ ing specially the larynx ; (6) the heart ; (c) a portion of the digestive tube, namely, the base of the tongue, the velum palati, the pharynx, oesophagus, stomach, and probably the duodenum ; (&amp;lt;/) it confers muscular sensibility on the muscles to which it is distributed ; (e) the mucous membrane of the biliary passages ; (/) a part of the dura mater corresponding to the transverse and occipital sinuses ; (g) the posterior part of the auditory canal. By the laryn- geal branches it specially stimulates expiratory movements. (B) It is motor to (.) many of the muscles of the palate ; (b) the constrictors of the pharynx ; (c) the oesophagus ; (d) the larynx by (a) the superior laryngeal to the crico- thyroid muscle and a portion of the arytenoid, and by (^3) the inferior or recurrent laryngeal to the rest of the muscles of the larynx ; and (e) to the muscular fibres of the bronchial tubes. (C) It contains vaso-inhibitoiy fibres for the heart. In connexion with this organ the vagus also contains sensory fibres and fibres belonging to the depressor system. (D) It influences secretion in the stomach (see NUTRITION) ; but it is doubtful whether it has any action on the renal secretion. (E) It influences the production of glycogen in the liver (see NUTRITION). 11. The spinal accessory is a motor nerve supplying the sterno-cleido-mastoid muscle and the trapezius. It gives an important branch to the vagus (internal branch), which supplies all the motor fibres in that nerve distributed to the larynx, except those in the superior laryngeal supplying the crico - thyroid muscle, and also the motor fibres of the vagus sent to the pharynx. Accord ing to Heidenhain, it also supplies the vagus with the inhibitory cardiac fibres. 12. The hypoglossal is exclusively a motor nerve supplying the muscles of the tongue and also the sub-hyoid muscles (see ANATOMY). It also contains vaso-motor filaments. SPINAL NERVES. The spinal cord gives origin in its course to thirty-one pairs of spinal nerves, each nerve having two roots, anterior and posterior, the latter being distinguished by its greater thickness and by the presence of an enlargement called a ganglion, in which are found numerous bi-polar cells. The anterior root is motor, the posterior sensory. The mixed nerve after junction of the roots contains sensory fibres passing to the posterior roots ; (b) motor fibres com ing from the anterior roots ; (c) sympathetic fibres, either vaso- motor or vaso-dilator. SYMPATHETIC SYSTEM. The fibres of the sympathetic system consist of two kinds (1) of grey or gelatinous fibres, destitute of the white substance of Schwann ; and (2) of medullated fibres similar to those met with in the cerebro - spinal centres. The grey fibres originate in the ganglia so prevalent in the sympathetic system, whilst the medullated fibres are believed to come from the cerebro -spinal system. The trunk of the great sympathetic nerve consists of a chain of swellings or ganglia, connected by intermediate cords of grey nerve-fibres, and extending nearly symmetrically on each side of the vertebral column, from the base of the cranium to the coccyx. On this part of the nerve twenty-four ganglia are placed on each side. This great trunk, as it passes along the spine, is connected with the spinal nerves, the connecting fibres being of the two kinds already described. The grey fibres dominate in the sympathetic nerves, and the medullated in the cerebro-spinal ; and these two elements are mixed in various proportions in both of the great divisions of the nervous system. At their lower extremities the main trunks of opposite sides generally unite in the middle line ; and at the upper ends each trunk, after being connected with the eighth and ninth cranial nerves, extends to the cranium, passes into that cavity along with the internal carotid artery, and there, as well as in other situations, comes into connexion with all the remaining cranial nerves, except the olfactory, auditory, and optic. This conjunction may be effected directly, as with the fourth, sixth, and ninth nerves ; or through a ganglion, as the ophthalmic, with the third and fifth ; the spheno-palatine, otic, and sub-maxillary, with the fifth and seventh, or facial ; the geniculate, with the seventh or facial ; the jugular, with the glosso-pharyngeal ; and with the vagus, through one of its own ganglia. On the fibres of the sympathetic distributed to the viscera numerous ganglia, or plexuses in which ganglia exist, are met with, and frequently there is a plexus following the course of each vessel. As to the functions of the sympathetic, experiment has led to Func- the following conclusions. tions of (a. ) The vaso-motor fibres of the head are supplied by the cervical sympa- portion of the sympathetic, and originate in the cervical region of thetic. the cord, proceeding from it by the anterior roots of the lower cervical and upper dorsal nerves. The fibres supplying the radiat ing fibres of the iris also come from that region (see EYE). (b. ) The vaso-motors of the upper limbs and of the thorax come (a) from the inferior cervical and superior thoracic ganglia, and (/3) from the cord, by communicating branches between the third and seventh dorsal vertebra?. (c. ) The vaso-motor fibres of the lower limbs come from the cord through the sciatic and crural nerves, whilst those of the pelvic organs are derived from the abdominal ganglia of the sympathetic. (d. ) The vaso-motors of the abdominal viscera exist chiefly in the splanchnic nerves ; some fibres supplying the stomach appear to be derived from the pneumogastric. (e. ) The splanchnic nerves all arise in man from the thoracic ganglia of the sympathetic the greater splanchnic from the fifth to the tenth ganglia, the lesser splanchnic from the tenth and eleventh, and the smallest splanchnic from the twelfth ganglion. The splanchnics supply the stomach, liver, spleen, pancreas, intestines, and kidneys. Division causes dilatation of vessels ; irritation causes contraction of vessels, and appears also to arrest or inhibit peristaltic motions of the stomach and intestines. Probably they also contain secretory filaments. The functions of vaso-motor nerves have been already described. A very complete bibliography of works relating to the nervous system will be found in the Dictionnaire Encydopedique des Sciences Medicales, 2d ser., xii. p. 619. For the comparative anatomy of invertebrates consult Gegenbauer, Elements of Comparative Anatomy (trans, and rev. by F. Jeffrey Bell and E. Ray Lankester, London, 1878) ; for the comparative anatomy of vertebrates, Owen, Anatomy of Vertebrates (3 vols., London, 1866) ; for details in human anatomy, Quain, Elements of Anatomy (9th ed., ed. by Allen Thomson, E. A. Schiifer, and G. D. Thane, London, 1882); for general physiology, Foster, Text-Book of Physio logy (4th ed., London, 1S83) ; for special details in physiology, H. Beaunis, Nouveaux Elements de Physiologic Hmnaine (2d ed., Paris, 1881) ; (specially for the functions of the cranial nerves) Flint, Physiology of Man (vol. v., New York, 1872) ; Ferrier, On the Functions of the Brain (London, 1876, also new ed.) ; Meynert, &quot;On the Brain of Mammals,&quot; in Strieker s Manual of Human aiul Comparative Histology (vol. ii., the New Syd. Soc., London, 1872) ; Flechsig, Die Leitungsbahnen im Gehirn itnd Riickenmark dcs Menschen (Leipsic, 1876), also &quot;Zur Anatomie und Entwickelungsgeschichte der Leitungsbahnen im Grosshirn des Menschen,&quot; in Du Bois-Reymond s Archiv fur Anatomie (Leipsic, 1881); Gudden, &quot; Experimentaluntersuchungen iiber das peripherische und centrale Nervensystem,&quot; in Arch. f. Psychiatrie (vol. ii., 1869, p. 713); Hitzig, Untersuchungen iiber das Gehirn (new series, 1874) ; Goltz, &quot; Ueber die Verricht- ungen des Grosshirns,&quot; in Pfliiger s Archiv (1876), also &quot;The discussion on the localization of function in the cortex cerebri,&quot; in Trans, of Inter. Med. Cong. (vol. i., 1881, p. 218) ; Munk, Ueber die Functionen der Grosshirnrinde (Berlin, 1881) ; Ross, Treatise on the Diseases of the Nervous System (2d ed., London, 1883). (J. G. M.) PART III PHYSIOLOGY OF PLANTS. THE body of a plant, like that of an animal, consists of one or more structural units which are termed &quot;cells,&quot; and in plants, as in animals, the cell consists essentially of an individualized mass of protoplasm. The probable structure and chemical composition of protoplasm have been already considered. It need only be stated here that the protoplasmic cell-contents do not consist of pure protoplasm, but that the protoplasm con tains imbedded in it particles of various substances which may be of the nature of food, or which may have been formed from food, or which are products of the metabolism of protoplasm ; it is to the presence of these particles that the granular appearance of protoplasm is largely due. Moreover, there is present in the protoplasm of the cell, in the vast majority of cases at least, a well-defined, highly- refractive, usually somewhat spherical body, also proto plasmic in nature, the nucleus. The cell or cells constituting the body of a plant pre- Cell- sent, in most cases, the important peculiarity that the walls, protoplasm is enclosed in a membrane termed the &quot; cell- wall.&quot; This membrane does not consist of protoplasm, but of a substance, cellulose, belonging to the group of the carbohydrates, and having the formula X^HjoOj. All cell-walls do not, however, consist exclusively of this sub-