VKRYOU8 8T8TKH. 



NERVOUS SYSTKSt 



16 



aM ^ the cU.n of 



MUM ef UM klter. IV 



**d there b 



Thbl 



>bno< 



b the flillill|llil Alb, which eonabte ef the meduUa 



IT-..- : .: 

 !.. . faM 



l>... 1 . I... 



DO oMopbageal 

 ; but UM two 



lateral etreoaV. ef the omelo spinel axb atill diverge from each other 

 m the* nrter the cranium, ao as to beve the epnee which b termed 

 hs ifcirth ventricle. Thb emrity commimbeles anteriorly with the 



the lateral halve* of the anterior 

 ; and posteriorly with the spinal 

 the two lateral halves of the spinal 

 . Uke the spec* between UM lateral halve* of 



the ventral obord in the higher 4rf.ce/ele. b nearly obliterated in man 

 sad the JreMte/M. although eumcieatly distinguishable in Fishes. 

 TUmhleioriGaniliteofa<MUnM>ejstrartofgraynatter. inclosed 

 i ef limgitndinal fibre*; and it may thu* be regarded 

 to the genjHenln chain ef the Arti^Uu. Below the 

 appear nearly similar throughout, 

 m it arc distributed to the sensory 

 the locomotive organ*. Ia some ferteireJe, whose 

 that ef the IrttcWefe (such as the eel and serpent), 

 ICM* m the ate* or distribution of the eereral pairs of 

 eerres, as no extremities an developed; but in other oases, the sUe of 

 the trunk*, pi limiting to the aoierior and posterior extremities, i* 

 SMhgri ell r then that of the nerres given off from the other seg- 

 meeto of the chord; end the quantity of gray matter at their note b 

 i leetnaiHq.Ay moreae.1. In these truniVboth afferent and efferent 

 ibre* are bound up; but they separate at their root*, or junction 

 with the spinel chord -the aflerent being connected with the side of 

 the chord Menet UM anrfao* of the back-end the motor with that 

 next the vbeera. Both Uissi root* have two sete of connection*; 

 some of each eater the grey substance of the chord, in which they 

 seem bet, whOet others ere continuous with the fibrous portion of the 

 chord, eod are thu* put in connection either with other segment* or 

 wish UM eareohalic centre*. In thi* respect, then, there b a precise 

 hate-inn the spinal column of I'erUorote and the 

 ef innate; and in the former, as in the latter, 

 of the chord has a certain 



ef ba-saaeisnni, reflex action* being excitable through it, ao 

 i ef aflerent and motor nerres, and their ganglionic 

 even though it be corn- 

 the upper portion of the 

 if ganglionic enlargement*, 



herb* eeterel distinct tuactione. From UM medulla oblongata pro- 

 ceed the chief nerve* which are subservient to the respiratory actions, 

 those MCeresJ in msetlostton awl deglutition j so that this 

 easy be regarded a* oomhrnrng the respiratory and the .tomato-gastric 

 Above, or m front of thb again, we find auditory, optic, and 

 to the various subdivision* of the 

 these receive trunks from their 



aee.Ha, are m an active and uninjured state, 

 pletcly spara>id from all the rest At U 

 spmei chord however, there b a series of | 



lljiai of aaml|nn. and nuy probably be regarded a* 

 maitiat, or acate of imainlnuajni for UM impreeaion* which 

 nO* tnaemtt The omnio-aninal *xi* oonatitutre the whole 



nrnej* Ijalim ef Amflutnt, in which there wem* nothing that in 

 UM Miat iiialle* a cerebrum, or cerrebellum , and among the 

 ecUetoea* kehe* (eMrally, the condition of thi* apparatu* i* but 

 Wttehajher. aa*e a* regarde the lannr derelopment of the aenior* 



.: ii 



D OH End 



Be* ia en UgWt rerteVtfe we find euperimpoeed (as it 

 the sensory gatjgte the bodies erhbh are known as tl 



re* or Oenglb; whilst superimposed upon the medulla 

 An4 the Cerebetlam. The former eoaetltute the mass 

 etiog-in and obscuring the sensory 

 idemental importance of these b 

 L U Ashes however the proportion 

 b entirely reversed, the rudiment* of 

 : usaally inferior In else to the optic 



I prinut m with a ninnsasluu 



ef gteiietlin. frsm the CM type to the other, a* regard* not merely 

 the ate* ef the *-tbrum. but also ite complexity oTetructur.; and 



ef the brain M the Jt 

 pavU.Moo.pbuly.that 

 by no meaae guiially reeog 

 ithetweeeteef 



erf the degree of intelligence of the apeatea. It b 

 (etaily worth* ef ante, that no sensory nerrcs 

 the cerebrum, MT do nay motor nerve* bene 



miii i ereey te orrebrum, nor do any motor nerre. ben* 

 Mrtty frM, M; ei thrre eaeaM a etrong probability that there b 

 nM lee w f.rwdy ppoa*)) a direct eooUnuity between any of the 

 *^nb <btrfrate4 to the body and the medullary aabrtaoce of 



medullary i 



of epseial sen** have thrir own 

 that the nervous fibre* 

 a* part of the 



part of the group of 

 *> forth freei the 



rtmU . whidi, Uke UM - 



So the 



either Into the 

 ef the spinal chord. 

 ee erigM higher than the corpora 

 are moat eesoredly to be regarded 



though formerly I 

 we ahall find atrong phy 

 cerebrum ha* no oomrounii 



considerable independence of the 

 as mere appendages to it And 

 ground for the belief that the 

 with the external world otherwise 

 tus which ministers to the automatic 



thu by the eenaori-motor apparatu 

 action*; receiving through the aenaorr ganglia that oonwiouinaM of 

 ' >bjecU and event*, which i* the ipriug of it* intellectual or 



tten 



operation*; and communicating it* voluntary ileteruiiua- 



to the motor part of the aame lyttem, to be worked-out (*o to 



peak) by it through the initrumeutality of the mtucle* upon which 

 t play*. The cerebellum, in like manner, preaenta a great difference 

 n relative development in the several clia*** of Ycrtcbraia ; being in 

 ihe loweat a mere thin lamina of uervous matter on the median line, 

 only partially covering in the fourth ventricle ; whilst in the highest 

 it i* a nuu* of considerable size, having two lateral Ijbes, or herui- 

 aphtrea, in addition to ita central portion. It U connected with both 

 the anterior and the potterior column* of the spinal chord ; and experi- 

 ment lead* to the belief that it* chief office i* to combine the individual 

 of different member* into the complex and nicely-balanced 

 rat* required for progression of various kinds, and in man for 

 the execution of the variou* operation* which hi* intelligence prompts 

 liiui to undertake. (Carpenter.) 



The part of the nervous lystem of the Vertebrala which is subject 

 to most alteration b the Brain. The chief differences in ita form 

 depend on the degree in which the hemisphere* of the cerebrum and 

 cerebellum are developed. In fishes these are usually smaller than 

 the ganglia on the origin of the optic nerves ; but ascending in the 

 scale they become more and more predominant in size over the rest of 

 the nervous centres, and appear to have a certain relation to the 

 development of intelligence in the animal. In the highest animals 

 and in man the lobe* of the cerebrum and cerebellum are by far the 

 largest of all the nervous organs ; their *urface are convoluted and 

 farrowed, the quantity of the gray matter upon them augmented, and 

 the complexity of their structure greatly increased. But as a special 

 article is devoted to thi* subject [BitAix], it need not be further cun- 

 lidered here ; for similar reason* we shall here treat of only the general 

 phenomena and law* of the action* of the nerve* a* they are observed 

 in man, and the cerebro-apinal system only in reference to the nerves 

 of common sensation and motion ; referring for the description of the 

 special senses to the article* EYE, EAR, NOSE, and TO.XUUB, and for 

 the peculiar influence of the nervous system in the most important 

 organs, to the article* devoted to them. [HEART ; STOMACH.] 



The constant functions of the cerebro-spiual nerves are to convey 

 impressions made on the points in which they are distributed, to the 

 brain, where they are perceived as sensations, or to the spinal chord, 

 where they are perceived without sensation ; and to convey the influence 

 of the will from the brain, or some involuntary influence from it or 

 the spinal chord, to the muscle* by which some motion is to be per- 

 formed. The influences that thus pass to and from the brain are 

 conveyed through distinct nervou* filaments, though the filaments 

 lubeervient to each are generally inclosed in the same sheath, and 

 appear to form a single and simple nerve. The filaments which convey 

 impressions to the nervous centres are called sensitive, centripetal, or 

 afferent; while those conveying impression* from the centres to the 

 muscle* are named motor, centrifugal, or efferent filaments. 



The spinal chord, in which all the nerves of the trunk have their appa- 

 rent origin, is composed of two lateral halves, symmetrical in form and 

 aim, and united together by a part of their inner surfaces at the median 

 line. The outer portion of the chord is composed of white nervous 

 matter, the inner of gray, an arrangement the reverse of that of the 

 brain, in which the cortical substance is gray, and the medullary or 

 central white. Each latent half of the spinal chord is again obscurely 

 divided by superficial furrow* into an anterior and a posterior column, 

 and a smaller middb portion between them. All the nerve* by which 

 enaitive impressions pass arise from the groove between the p<>- 

 and middle columns, and all those (with the exception of the spinal 

 accessory nerve) by which the excitants to muscular motion are con- 

 veyed aria* from the groove between the anterior and middle columns. 

 They all arbe by what are called roots, that is, by a number of fine 

 nervous threads or narrow bands attached to the grooves, and passing 

 fur a short distance into the substance of the chord, which, as they 

 proceed outwards, converge and unite into a single chord or nerve. 

 There is an important dintiiiction however between them : the roots 

 of the posterior or sensitive nerves have a ganglion at their union just 

 when they are baring the vertebral canal, while those of the anterior 

 or motor nerve* unite without any ganglion into a single chord, v\ !,.. h 

 passe* over but doe* not communicate with the ganglion on the pos- 

 terior roots. Beyond this ganglion the anterior and posterior roota 

 unite in a common sheath, iu which their filament*, though 

 continue distinct, are indiscriminately mixed; and in Ibis manner 

 they proceed through the varied branching* of the sheath to nearly 

 all parts of the body, conveying the power of perceiving impressions 

 to all. and the power of motion to the muscles and probably a few 

 - 



Nearly the seme mode of origin and distribution, and the same dis- 

 tinctness of office, are foun-l in the nerves that have their centre in 

 the brain, in which tboe of the fifth pair [BBAIK] are almost exactly 

 analogous to the spinal nerve*. But in the other cerebral nerves there 



