See also:

• NERVE (Lat. nervus, Gr. vevpov, a bowstring)

NERVE (See also:

• LAT

Lat. nervus, Gr. vevpov, a bowstring)  , originally a See also:

• SINEW (O. Eng. sinu, sionu, cf. Dutch zenuw, Ger. Sehne, possibly allied to Skt. snava, tendon, cf. Ger. Schnur, string)

sinew or tendon (and still so used in the phrase " to See also:

• STRAIN (through O. Fr. straindre, estraindre, mod. i treindre, from Lat. stringere, to draw tight, related to stress, stretch, string, &c.)

strain every See also:

• NERVE (Lat. nervus, Gr. vevpov, a bowstring)

nerve "), but now a See also:

• TERM

term practically confined to the See also:

• FIBRES
• FIBRES (or FIBERS, in American spelling; from Lat. fibra, apparently connected either with filum, thread, or findere, to split)

fibres of the See also:

• NERVOUS

nervous See also:

• SYSTEM

system in See also:

• ANATOMY
• ANATOMY (Gr. avaroyil, from ava-silo c', to cut up)

anatomy, though consequentially employed as a See also:

• GENERAL
• GENERAL (Lat. generalis, of or relating to a genus, kind or class)

general psychical term in the sense of courage or firmness, and sometimes (but more usually " nervousness ") in the opposite sense . In the See also:

• PRESENT

present See also:

• ARTICLE (from Lat. articulus, a joint)

article the anatomy of the nerves is dealt with; see also NERVOUS SYSTEM, MUSCLE AND NERVE, See also:

• NEUROPATHOLOGY

NEUROPATHOLOGY, &c . I . See also:

• CRANIAL

CRANIAL The cranial nerves are those which rise directly from the See also:

• BRAIN (A.S. braegen)

brain, and for the most See also:

• PART

part are concerned with the See also:

• SUPPLY (through Fr. from Lat. supplere, to fill up)

supply of the See also:

• HEAD (in 0. Eng. heafad; the word is common to Teutonic languages; cf. Dutch hoofd, Ger. Haupt, generally taken to be in origin connected with Lat. caput, Gr. KerbOvi7)
• HEAD, SIR EDMUND WALKER, BART
• HEAD, SIR FRANCIS BOND, BART

head . With one exception they all contain medullated fibres (see NERVOUS SYSTEM) . Twelve pairs of these nerves are recognized, and they are spoken of as often by their See also:

• NUMBERS, BOOK OF
• NUMBERS, PARTITION OF

numbers as by their names . The following is a See also:

• LIST (O.E. lisle, a Teutonic word, cf. Dut. lust, Ger. Leiste, adapted in Ital. lista and Fr. lisle)
• LIST, FRIEDRICH (1789-1846)

list: (I) Olfactory; (2) Optic; (3) Oculo-motor or Motor oculi; (4) Trochlearis or Patheticus; (5) Trigeminal or Trifacial; (6) Abducens; (7) Facial; (8) Auditory; (9) Glosso-pharyngeal; (to) Vagus or Pneumogastric; (1r) See also:

• SPINAL

Spinal See also:

• ACCESSORY

accessory; (12) Hypoglossal . The first, or olfactory nerve, consists of the olfactory bulb and See also:

• TRACT (from Lat. tractare, to treat of a matter, through Provencal tractat and Ital. trattato)

tract, which are a modified See also:

• LOBE

lobe of the brain and See also:

• LIE, JONAS LAURITZ EDEMIL (1833—1908)
• LIE, MARIUS SOPHUS (1842–1899)

lie beneath the sulcus rectus on the frontal lobe of the brain (see fig . I) . At its posterior end the tract divides to become continuous with the two extremities of the limbic lobe (see BRAIN), while at its anterior end is the bulb from which some twenty small non-medullated nerves pass through the cribriform See also:

• PLATE

plate of the ethmoid to supply the sensory See also:

• ORGANS

organs in the olfactory mucous membrane (see OLFACTORY See also:

• ORGAN

ORGAN) . The second or optic nerve consists of the optic tract, the optic commissure or chiasma, and the optic nerve proper . The optic tract begins at the See also:

• LOWER

lower visual centres or See also:

• INTERNAL

internal and See also:

• EXTERNAL

external geniculate bodies, the See also:

• SUPERIOR

superior quadrigeminal See also:

• BODY

body and the pulvinar (see fig .

I), but these again are connected with the higher visual centre in the occipital lobe by the optic radiations (see fig . 2) . In the chiasma some of the fibres See also:

• CROSS

cross and some do not, so that the right optic tract forms the right See also:

• HALF

half of both the right and See also:

• LEFT

left optic nerves . In addition to this the fibres coming from the internal geniculate body of one See also:

• SIDE
• SIDE (mod. Eski Adalia)

side cross in the chiasma to the same body of the opposite side, forming Gudden's,commissure . The optic nerve passes through the optic foramen in the See also:

• SKULL

skull into the See also:

• ORBIT (from Lat. orbita, a track, orbis, a wheel)

orbit, where it is penetrated by the central artery of the retina, and eventually pierces the scelerotic just internal to the posterior See also:

• POLE (FAMILY)
• POLE, REGINALD (1500-1558)
• POLE, RICHARD DE LA (d. 1525)
• POLE, WILLIAM (1814—1900)

pole of the eyeball . Its final See also:

• DISTRIBUTION (Lat. distribuere, to deal out)

distribution is treated in the article See also:

• EYE
• EYE (O. Eng. edge, Ger. Auge; derived from an Indo-European root also seen in Lat. oc-ulus, the organ of vision (q.v.)

EYE . The third or oculomotor nerve rises from a See also:

• NUCLEUS (Lat. for the kernal of a nut, nux, the stone of fruit)

nucleus in the See also:

• FLOOR (from O. Eng. flor, a word common to many Teutonic languages, cf. Dutch vloer, and Ger. Flur, a field, in the feminine, and a floor, masculine)

floor of the See also:

• AQUEDUCT (Lat. aqua, water, and ducere, to lead; Gr. apaymryeiov, apayeeywov, vlrovopos)

aqueduct of Sylvius (see BRAIN, fig . 8), and comes to the See also:

• SURFACE

surface in a groove on the inner side of the crus cerebri (fig . I); it soon pierces the dura mater, and lies in the See also:

• OUTER

outer See also:

• WALL (O. Eng. weal, weall, Mid. Eng. wal, wane, adapted from Lat. vallum, rampart; the original O. Eng. word for a wall was wag or tenth)
• WALL, RICHARD (1694-1778)

wall of the cavernous sinus, where it divides into an upper and lower See also:

• BRANCH (from the Fr. branche, late Lat. branca, an animal's paw)

branch . Both these enter the orbit through the sphenoidal fissure, the upper branch supplying the superior rectus and levator palpebrae superioris muscles, the lower the inferior and internal rectus and the inferior oblique, so that it supplies five of the seven orbital muscles . The See also:

• FOURTH

fourth or trochlear nerve is very small, and comes from a nucleus a little lower than that of the third nerve . It is specially remarkable in that it crosses to the opposite side in the substance of the See also:

• VALVE (Lat. valva, a leaf of a double or folding door, allied to volvere, to roll, as of a door on its hinges)

valve of Vieussens of the fourth ventricle, after which it winds See also:

• ROUND (O. Fr. rond, Lat. rotundus, the Fr. is the source also of Du. rond; Ger., Swed., Dan. and Nor. rond)

round the outer side of the crus cerebri (fig. i) and enters the outer wall of the cavernous sinus to reach the orbit through the sphenoidal fissure .

Here it enters the superior oblique muscle on its orbital surface . The fifth or trigeminal nerve consists of motor and sensory roots . The motor See also:

• ROOT (late O.E. rot, adopted from Scand., cf. Norw. and Swed. rot, Dan. rod; the true O.E. word was wyrt, plant, represented in Ger. Wurz or Wurzel; the ultimate root is the same in both words, and is seen in Lat. radix)
• ROOT, ELIHU (1845– )

root rises from a nucleus in the upper lateral part of the floor of the fourth ventricle, as well as by a descending (mesencephalic) tract from the neighbourhood of the Sylvian aqueduct (see fig . 3) . The large sensory root goes to a sensory nucleus a little external to the motor one, and also, by a spinal or descending root, to the substantia gelatinosa Rolandi as See also:

• LOW, SETH (1850- )
• LOW, WILL HICOK (1853- )

low as the second spinal nerve (see fig . 3) . The su rficial origin of the fifth nerve is from the side of the pons (see f g . I), and the two roots at oncepass into a small compartment of the dura mater, in front of the See also:

• APEX

apex of the petrous See also:

• BONE (a word common in various forms to Teutonic languages, in many of which it is confined to the shank of the leg, as in the German Bein)
• BONE, HENRY (1755-1834)

bone, known as Meckel's See also:

• CAVE (Lat. cavea, from caves, hollow)
• CAVE, EDWARD (1691–1754)
• CAVE, WILLIAM (1637–1713)

cave; here the large crescentic Gasserian ganglion is formed upon the sensory root, and from this the three branches come off, earning the nerve its name of trigeminal . The first of these divisions is the ophthalmic, the second the maxillary, and the third the mandibular, while the motor root only joins the last of these . The first or ophthalmic See also:

• DIVISION (from Lat. dividere, to break up into parts, separate)

division of the fifth runs in the outer wall of the cavernous sinus, where it divides into frontal, lachrymal and nasal branches . They all enter the orbit through the sphenoidal fissure . The frontal nerve divides into supraorbital and supratrochlear, which pass out of the upper part of the anterior opening of the orbit and supply the skin of the forehead and upper part of the See also:

• SCALP (0. Dutch schelpe, a shell)

scalp as well as the inner part of the eyelids .

The lachrymal nerve supplies that gland and the outer part of the upper eyelid . The nasal nerve gives off a branch to the ciliary or lenticular ganglion, which lies in the outer part of the orbit, and through which, as well as through its own See also:

• LONG, GEORGE (1800-1879)
• LONG, JOHN DAVIS (1838– )

long ciliary branches, it supplies the eyeball with sensation . It leaves the orbit through the anterior eth- moidal See also:

• CANAL
• CANAL (from Lat. canalis, " channel " and " kennel " being doublets of the word)

canal, and lies for a See also:

• SHORT, FRANCIS JOB (1857– )

short distance on the cribriform plate of the ethmoid ; it then enters the nasal cavity through the nasal slit and supplies this cavity, as well as the surface of the See also:

• NOSE (O.Eng. nosu, cf. Dutch neus, Swed. nos, snout; the Aix in Provence. Both at Aix and at Lyons he acquired great connexion with O.Eng. nasu is obscure, cf. Ger. Nase, Lat. pares, distinction by his labours during outbreaks of the plague. In nostrils,

nose as far as the tip, with See also:

• ORDINARY (med. Lat. ordinarius, Fr. ordinaire)

ordinary sensation . The second or maxil- lary division of the fifth nerve leaves the skull through the foramen rctundum, and then runs across the roof of the spheno-maxillary fossa; here the spheno-maxillary or Meckel's ganglion hangs from it by two roots . The nerve then runs in the floor of the orbit, giving off superior dental branches, until it emerges on to the See also:

• FACE (from Lat. fades, derived either from facere, to make, or from a root fa-, meaning " appear "; cf. Gr. cbatvstv)

face at the infraorbital foramen, where it divides into palpebral, nasal and labial branches, the names of which indicate their distribution . The third or mandibular division of the fifth leaves the skull through the foramen ovale, and .at once gives off a set of motor branches for the muscles cf mastication; these are derived from the motor root of the fifth, except that for the buccinator, which really supplies only the skin and mucous membrane in contact with the muscle . After the motor branch is given off, the third division of the fifth divides into, lingual, inferior dental and auriculo-temporal . The lingual is joined by the chorda tympani branch of the facial nerve, and then passes to the anterior two-thirds of the See also:

• TONGUE (O. Eng. lunge)

tongue . In its course it passes deep to the submaxillary gland, and here the small sub- maxillary ganglion is connected with it by two roots . The inferior dental nerve gives off a small motor branch to the mylohyoid and posterior belly of the digastric muscles, and then enters a canal in the lower See also:

• JAW (Mid. Eng. jawe, jowe and geowe, O. Eng. cheowan, connected with " chaw " and " chew," and in form with " jowl ")

jaw, where it gives off twigs to all the lower See also:

• TEETH (O.E. Eel); plural of tooth, O.E. top)

teeth . A See also:

• MENTAL

mental branch comes out through the mental foramen to supply the skin of the See also:

• CHIN

chin . The auriculo temporal nerve rises by two roots, which embrace the See also:

• MIDDLE

middle meningeal artery, and runs backward and then upward See also:

• CLOSE
• CLOSE (from Lat. clausum, shut)
• CLOSE, MAXWELL HENRY (1822-1903)

close to the lower jaw See also:

• JOINT (through Fr. from Lat. junctum, jungere, to join)

joint to supply the parotid gland, the skin on the outer side of the See also:

• EAR (common Teut.; O.E. are, Ger. Ohr, Du. oor, akin to Lat. auris, Gr. ovs)

ear, and the side of the scalp .

At its beginning it communicates with the otic ganglion, which lies just internal to it below the foramen ovale, and also receives a communication from the nerve to the internal pterygoid muscle . The See also:

• SIXTH

sixth or abducent nerve rises from a nucleus in the floor of the fourth ventricle deep to the eminentia teres (see fig . 3) . It appears on the surface of the brain just below the pons and close to the middle See also:

• LINE

line (see fig . I), soon after which it pierces the dura mater and runs in the floor of the cavernous sinus to the sphenoidal fissure . Entering the orbit through this, it quickly supplies the external rectus muscle . The seventh or facial nerve begins in a nucleus which is about the same level as that for the sixth, but much deeper from the floor of the fourth ventricle as well as farther from the middle line (see fig . 3) . The fibres of. the facial See also:

• LOOP

loop round the nucleus of the sixth, and then emerge in the triangular See also:

• INTERVAL

interval between the medulla, pans and cerebellum, close to the eighth nerve. and having the pars Oculo-motor nerve Trochlear nerve Trigeminal nerve Abducent new Facial nerve Pars intermedia Auditory new Glosso-pharyngeal nerve Vagus nerve Spinal accessory nerve (accessory) Spinal accessory nerve (spinal) Hypoglossal nerve Hypoglossal nerve Spinal See also:

• CORD (derived through the Fr. corde, from the Lat. chorda, Gr. xop(5rt, the string of a musical instrument)

cord Vermis of Cerebellum (cut) Olfactory tract See also:

• BROCA, PAUL (1824-188o)

Broca's See also:

• AREA

area Olfactory tubercle Mesial root of olfactory erve Lateral root Optic chiasma See also:

• ANT
• ANT (O. Eng. aemete, from Teutonic a, privative, and maitan, cut or bite off, i.e. " the biter off "; aemete in Middle English became differentiated in dialect use to (mete, then amte, and so ant, and also to emete, whence the synonym " emmet," now only u

Ant. perforated spot Temporal lobe (cut) Optic tract Oculo-motor nerve Trochlear nerve See also:

• TAENIA (Gr. Tatyla, ribbon, fillet)

Taenia semicircularis Trigeminal nerve See also:

• EXT

Ext. geniculate body Abducent nerve Int. geniculate body Pulvinar Facial nerve Pars intermedia Auditory nerve Lateral ventricle See also:

• MID

Mid. cerebellar peduncle Glosso-pharyngeal nerve Vagus nerve Spinal accessory nerve (accessory) Spinal accessory nerve (spinal) Occipital lobe (cut) From D . J . See also:

• CUNNINGHAM, ALEXANDER (c.1655-173o)
• CUNNINGHAM, ALLAN (1784-1842)
• CUNNINGHAM, WILLIAM (1805-1861)

Cunningham, in Cunningham's See also:

• TEXT (Lat. textum, woven fabric, from texere, to weave)

Text-See also:

• BOOK

book of Anatomy . lobes, and the cerebellum on the left side removed, to show the origins of the cranial nerves .

intermedia between (see fig . O . Entering the internal auditory meatus with these structures the facial nerve soon passes into a canal in the petrous bone known as the aqueductus Fallopii, and in this it makes a sudden See also:

• BEND

bend and forms the geniculate ganglion, from which the See also:

• GREAT

great superficial petrosal branch to Meckel's ganglion is given off . The canal ends at the stylo-mastoid fora- men on the See also:

• BASE

base of the skull, and here the nerve enters the parotid gland, in which it forms a plexus called the pes anserinus . From this, branches pass to all the muscles of the face except those of mastication . In the aqueduct the pars intermedia joins the seventh, and, beyond the geniculate ganglion, leaves it as the chorda tympani, o which runs through the tympanum (see EAR) to join the lingual branch of the fifth . It is probable that the pars intermedia, geniculate ganglion and chorda tym pani, represent the sensory root of the facial nerve . Just out-1O96 side the stylo- mastoid foramen From D . J . Cunningham, in Cunningham's Text-Book of the facial gives Anatomy. off the poslei for FIG . 2.-See also:

• DIAGRAM

Diagram of the Central Connexions auricular branch of the Optic Nerve and Optic Tract. to the occipitalis and posterior auricular muscles, as well as a branch of supply to the etylohyoid and posterior belly of the digastric muscles . The eighth or auditory nerve is in two bundles, cochlear and vestibular .

The former comes from the cochlear nuclei which lie deep to the acoustic tubercle in the floor of the fourth ventricle (see fig . 3), while the latter rises from the dorsal nucleus, nucleus of Deiters and the nucleus of the descending root, which are more deeply placed . The nucleus of Deiters is connected with the cerebellum, and is concerned in maintaining the See also:

• EQUILIBRIUM (from the Lat. aequus, equal, and libra, a balance)

equilibrium (q.v.) of the body, while, as is pointed out in the article BRAIN, the cochlear nuclei are connected with the inferior quadrisphenogeminal body o lodybe by by the the aulateralditory See also:

• FILLET (through Fr. filet, from the med. Lat. filettum, diminutive of filum, a thread)

fillet as radiations. asons. with The the vestibular internal ts~~r,, ,E 7 niculate body, while this body again is connected with the her auditory centre in the See also:

• GREY, CHARLES GREY, 2ND EARL (1764-1845)
• GREY, HENRY GREY, 3RD EARL (1802-1894)
• GREY, LADY JANE (1537-1554)
• GREY, SIR EDWARD
• GREY, SIR GEORGE (1812–1898)

grey cortex of the temporo- cocHLcon N TUB, wcusr,cuM ago so \ root passes in front of the restiform body (see fig . 3), and the P''An' cochlear behind that body . Together they enter the internal ruci.cus AMe auditory meatus, and, at the end of it, See also:

• PIERCE, FRANKLIN (1804—1869)

pierce the lamina cribrosa. the vestibular nerve supplying the utricle and superior and external semicircular canals, the cochlear nerve the posterior canal, the saccule and the cochlea (see EAR) . The ninth or glossopharyngeal nerve is chiefly, if not entirely, sensory, and its deep termination in the brain is the solitary bundle (see fig . 3; and BRAIN, fig . 4) . It appears on the surface between the See also:

• OLIVE (Olea europaea)

olive and restiform body (see fig . I), and leaves the skull through the posterior lacerated foramen ; as it does so two ganglia, the jugular and petrous, are formed on it, after which It runs downward and forward, between the internal and external See also:

• CAROTID

carotid See also:

• ARTERIES (Gr. ap-rnpia, probably from a"spew, to raise, but popularly connected by the ancients with ai7P, air)

arteries, and eventually reaches the back of the tongue (see TONGUE) . On its way it supplies the tympanum, the stylopharyngeus muscle, though there is See also:

• GRAVE

grave doubt as to whether these fibres are not really derived from the facial nerve, contributions to the pharyngeal plexus, the tonsil and part of the epiglottis . From D .

J . Cunningham, in Cunningham's Text-Book of Anatomy . . The tenth nerve or vagus has sensory and motor fibres; the FIG . 3.-Deep Origins of Cranial Nerves from the Fourth Ventricle. former go to the solitary bundle mentioned in the description of the last nerve (see fig . 3), while the latter come from the dorsal nucleus and nucleus ambiguus, both of which are found deep to the lower half of the fourth ventricle . The nerve appears on the surface between the olive and restiform body and just below the ninth (see fig . I) . It leaves the skull through the posterior lacerated foramen, and, like the glossopharyngeal, has two ganglia See also:

• DEVELOPED

developed on it; the upper of these is the ganglion of the root, and the lower the ganglion of the See also:

• TRUNK (Fr. tronc, Lat. truncus, cut off, maimed)

trunk (see fig . 4) . From the former the auricular branch or See also:

• ARNOLD
• ARNOLD, BENEDICT (1741-1801)
• ARNOLD, GOTTFRIED (1666-1714)
• ARNOLD, MATTHEW (1822-1888)
• ARNOLD, SAMUEL (1740--18o2)
• ARNOLD, SIR EDWIN (1832-1904)
• ARNOLD, THOMAS (1745-1842)

Arnold's nerve (see EAR) comes off, while from the latter are given off the pharyngeal branches to the pharyngeal plexus (fig . 4, Ph.) and the superior laryngeal branch which is the sensory nerve of the larynx (fig . 4, S.L.) .

Between the two ganglia the accessory part of the See also:

• ELEVENTH

eleventh nerve joins the tenth, and it is from this communication that the motor twigs to the pharynx, larynx, alimentary and See also:

• RESPIRATORY

respiratory tracts are derived, as well as the inhibitory fibres of the See also:

• HEART
• HEART, LUNG

heart . In the See also:

• NECK (O. Eng. hnecca; the word appears in many Teutonic languages; cf. Dutch ride, Ger. Nacken; in O. E. the common word was heals; cf. Ger. Hals)

neck the vagus accompanies the carotid artery and internal jugular vein, and here it gives off superior and inferior cardiac branches . The left inferior cardiac branch passes to the superficial, while the three others go to the deep cardiac plexus . The nerve now enters the See also:

• THORAX (Gr. BWpaE, breastplate, also the part of the body covered by it)

thorax, passing between the subclavian artery and vein . On the right side its recurrent laryngeal branch loops under the subclavian artery (fig. q., R.), and runs up to supply all the muscles of the larynx except one (see RESPIRATORY SYSTEM) . In the thorax the left vagus passes in front of the See also:

• ARCH
• ARCH, JOSEPH (1826– )

arch of the aorta, under which the left recurrent laryngeal loops, and on both sides a thoracic cardiac branch is given to the deep cardiac plexus . Both vagi pass behind the root of their own See also:

• LUNG

lung, and break up to See also:

• FORM (Lat. forma)

form the posterior pulmonary plexus after giving off some branches for the much smaller anterior pulmonary plexus; they then reach the See also:

• OESOPHAGUS (Gr. o'lvca=I will carry, and r/)ayeiv, to eat)

oesophagus, where they again break up into an oesophageal plexus or plexus gulae . As the See also:

• DIAPHRAGM (Gr. Scat/pay,aa, a partition)

diaphragm is approached the two nerves become distinct again, but the left one now lies in front and the right behind the See also:

• FOOD
• FOOD (like the verb " to feed," from a Teutonic root, whence O. Eng. foda; cf. " fodder "; connected with Gr. lrareicOae, to feed)

food See also:

• TUBE (Lat. tuba)

tube, so that, when the See also:

• STOMACH (Gr. vrbsaxos from arbga, a mouth)

stomach is reached, the left vagus supplies the front of the organ and communicates with the hepatic plexus, while the right goes to the back and communicates with the coeliac, splenic and renal plexuses . The eleventh or spinal accessory nerve is entirely motor, and consists of a spinal and an accessory part . The former rises from the anterior See also:

• HORN
• HORN (a common Teutonic word, cognate with Lat. cornu; cf. Gr. Kipas)
• HORN (Lat. cornu; corresponding terms being Fr. cor, trompe; Ger. Horn; Ital. corno)
• HORN, ARVID BERNHARD, COUNT (1664-1742)
• HORN, PHILIP DE MONTMORENCY, COUNT

horn of the grey See also:

• MATTER

matter of the spinal cord as low as the fifth cervical nerve . Its fibres come to the surface mid-way between the anterior and posterior nerve-roots, and run up through the foramen magnum to join the accessory part, the deep origin of which is the lower part of the nucleus ambiguus . The accessory part, as has been noticed, joins the vagus, while the spinal part pierces the sterno-mastoid muscle and runs obliquely downward and backward across the posterior triangle of the neck to enter the trapezius; both these muscles are in part supplied by the nerve .

The twelfth or hypoglossal nerve is motor, and rises from a nucleus in the floor of the fourth ventricle deep to the trigonum hypoglossi (see BRAIN, fig . 3) . It emerges from the brain between the anterior See also:

• PYRAMID

pyramid and the olive (see fig . I), and leaves the skull in two bundles through the anterior condylar foramen . Soon after this it is closely See also:

• BOUND, or BOUNDARY (from O. Fr. bonde, Med. Lat. bodena or butina, a frontier line)

bound to the vagus, and, in front of the See also:

• ATLAS

atlas, receives an important contribution from the loop between the first and second cervical nerves . The nerve then passes downward until it reaches the origin of the occipital artery, round which it loops, and then runs forward on the surface of the hyo-glossus to the muscles of the tongue . As it bends round the occipital artery it gives off its descendens hypoglossi branch, which derives its fibres from the communication with the first cervical already mentioned . This branch runs down and forms a loop with the communicans cervicis branch from the second and third cervical nerves, and from this loop (See also:

• ANSA (from Lat. ansa, a handle)

ansa hypoglossi) many of the depressor muscles of the hyoid bone and larynx are supplied . Farther forward See also:

• SPECIAL

special branches are given off to the thyro-hyoid and genio-hyoid muscles, and these, like the descendens hypoglossi, are derived from the first and second cervical loop, thus leaving all the true muscles of the tongue to be supplied by the medullary part of the nerve . For the See also:

• EMBRYOLOGY

embryology and See also:

• COMPARATIVE

comparative anatomy of the cranial nerves, see NERVOUS SYSTEM . Il.SPINAL The spinal nerves are those which arise from each side of the spinal cord and are distributed to the trunk and limbs, though some of the upper ones supply the lower parts of the head and face . As is shown in the article NERVOUS SYSTEM, the division between cranial and spinal nerves is rather one of convenience than of any real scientific difference .

There are generally See also:

• THIRTY

thirty-one pairs of these nerves, which are subdivided according to the part of the vertebral See also:

• COLUMN (Lat. columna)

column through which they pass out; thus there are eight cervical (abbreviated C.), twelve thoracic (Th.)—formerly called dorsal, five lumbar (L.), five sacral (S.) and one See also:

• COCCYGEAL

coccygeal (Coc.) . As the thoracic nerves are the simplest and most generalized in their arrangement, a typical one of these, say the fourth or fifth, will be first described . The nerve is attached to the spinal cord by two roots, of which the ventral is purely efferent or motor and the dorsal purely afferent or sensory . On the dorsal root is a fusiform ganglion which lies in the foramen be- tween the vertebrae through which the nerve passes . The two roots then join together to form a mixed nerve (see fig . 5), but very soon See also:

• DIVIDE

divide once more into anterior (ventral) and posterior (dorsal) See also:

• PRIMARY

primary divisions . These, however, each contain sensory and motor fibres .