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ANATOMY AND PHYSIOLOGY.

LECTURES

ILLUSTRATED BY THE

HUNTERIAN PREPARATIONS

IN THE MUSEUM OF THE ROYAL COLLEGE

OF SURGEONS, LONDON.

Delivered at the College in 1833, by

SIR CHARLES BELL, K. G. H., F. R. S.

LECTURE XIV.

THE NERVOUS SYSTEM.

GENTLEMEN,-In looking back uponthe subjects of this short course of lec-tures, we may find some that will assistus in our present more difficult task.You will remember that I stated it was

necessary that we should mark the differ-ence between animals, whether theybelong to the vertebrata, or to the lowerclasses, and that we had occasion to re-mark that the vertebrata were peculiar inthis respect, that they had a spine, andribs connected with it, muscles to movethose ribs, nerves to connect those mus-cles together, and a source of energy forthose nerves in the medulla spinalis.We had occasion, then, to remark thatanimals of the higher class were totallydifferent from those of the lower. Nowthis is an introduction to the subject onwhich I am about to speak, because thecondition for action is connected withthe condition of the whole frame.

Again, when we came to the muscles, we found, I might almost say innumerablemuscles, under the direction of the will; 1

but, perhaps, fifty muscles at least are i

drawn into one simultaneous action by the B will; and this must be accounted for with I ;a full understanding and acknowledgment ! Ithat there is no relation existing directly between or amongst the muscles them-selves, and, therefore, we must look forsome means by which they are combined. BThen we recollect that there is a class of muscles called flexors, and opposed to) these, or contrasted with them, there are Iextensors. A relation is established be- tween these, and that relation must be, Baccounted for by reference to some third!power, because a connexion is not com- Bmon among themselves. Then, again, when we had, as it were,

Iaccounted for the act of volition in the mo-tion of the body, we had reason to con-clude that the same muscles used in that

motion were brought into new com-bination, a combination which is with-drawn altogether from the influence ofthe mind, and the functions for whichthey were connected are secured by an-other source of action. So far we seethat there must be different nerves, withdifferent senses, which shall diverge, toproceed to and connect together the

several muscles.Now let me observe to you, that I con-

ceive that physiologists of great meritamongst us have erred in going direct totheir object when they made dissectionsof nerves, or experimented upon nerves,without sufficiently comprehending theuse of the nerves; that is to say, the func-tions necessary to be performed throughtheir means, or the combination which isnecessary in the performance of the se-veral functions of parts or organs. Ithink that some have lost themselves bygoing too direct to the object, instead ofdiligently studying the number of parts,for example, that must be associated in thesingle act of drawing breath, and the addi-tional association of parts when the act ofspeech is engrafted upon that of respira.tion. How many muscles must be addedto those employed in the single act of re-

spiration before the voice can be called; into exercise’; and how many more beforethe voice is articulated in language! Or,again,-as we have been more lately con-sidering,-how different the sensibilitymust be, and how different the arrange-ment of the muscles is, within the orbitof the eye ! Is it reasonable to expectthat we should account for the action orinfluence of the nerves which enter theorbit, if N,,7e have not previously diligentlystudied the functions which are to bethere performed ?

I do not know, then, that I can do betterthan recollect the manner in which I used

to express myself, being convinced that indoing so, I excited my young friends togreater diligence as students, and affordedthem some gratification.

I took up the subject in this way:-When the human body, for example, is’ preserved in spirits, and taken out forten or twelve hours in a day for dissection,and the dissection is continued for amonth or six weeks, what an extraordi-

e dinary exhibition of nerves is pre-- sented ! But the most remarkablething is, that if we take another body,1’ and dissect it with the same care, we shall- find the same parts precisely. And if,

again, you examine a third, every twig’, that was in the other two appears in this- one. You have, in the first body, a little- ganglion, a little knot, looking as if it

at were accidentally placed there ; and when

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you examine the second and third bodies;you still find it at the same spot, and hav-ing the same relations with other parts.

If you take up a nerve, say a little twig,which seems to be a mere individual partof a mesh, and look in the same direc-tion in two or three bodies, you will findthe same twig there also, in the same

place, with the same relations, and pre-serving the same connexion.Thus you see that the nerves are differ-

ent altogether from the bloodvessels.The arteries all proceed from the heart,but they may take a devious course, thebranch in one body going direct, in an-other going circuitously, or in a third youhave two or three branches performingthe one office. Nothing of this kind takesplace in the nerves ; the apparent irre-gularity in them is the effect of the imper-fection of our own observations ; they areperfectly regular; you cannot see a branchin one instance without seeing the same inanother body; you cannot find the smallesttwig bearing a relation to a particularnerve, but you will find it, if you go toother pieces of dissection, in every in-stance the same, and, therefore, our firstimpression that this is an accidentaltissue is at once removed. There is no-

thing at all irregular or accidental in it.On the contrary, we find enough to provethat there must be some system, an exactarrangement of parts, to explain whichpuzzles us, and we want a key to thedifficulty.

Exactly the same effect-one of dis-appointment on finding such regularity-strange as it may seem, occurs to thestudent, if he turn over the leaves, forexample, of BicHAT, WALTHER, MONRO,SCARPA, and now we may add our ownauthority, SWAN.The first thing that strikes us now is,

the extraordinary intricacy and difficultyof the subject, and we must, in somemanner, endeavour to remove it, and tofind the system which we are sure mustexist in consequence of the same vheno.mena presenting themselves in every in-stance. We find that even down to thetime of Dr. BAILLIE the same notion hasprevailed, and that a very natural one,that the brain was the centre of thenervous system,-that the brain was theofficina spiritacum,-that something wasthere secreted, or provided, which wentout by the tubera of the nerves, and wasconveyed and gave life to every part ofthe body.Now this is well enough so long as we

take a superficial view of the nervous sys-tem, because it seems that the nervous

power does thus diverge, and that the pro-perties of life are cut off by the depletion of

!,’ that particular nervous energy. But when- you come to the personal examination of

the body itself, then the facts are at total, variance with the hypothesis. What ist the meaning of one nerve crossing another- without joining it ? What is the mean-I ing of one nerve crossing and joining an-other ? You begin to discover that there= must of necessity either be differentsources of nervous energy, or different en-dowments leading through those nerves to. different parts. It cannot be that the, whole nervous power diverges from a

single part of the brain, and thence passesout to the several parts of the body. SuchI a supposition is inconsistent with what is5 discovered in dissections.! I In my endeavours to find some key, or. some circumstance, which should direct- me in this matter, 1 began by imagining;. that I could make something of the origini of the nerves by experimenting upon thebrain. Accordingly I made small per-

t forations in the skulls of animals, and

passed a fine needle and thread throughdifferent parts of the brain, imaginingthat in .that way I should inflame it,and produce a morbid influence on

[ several parts of it. I then proposed. to observe the effects, but was completely. disappointed in the attempt. I could;! make nothing of my experiments, and; could find no clue to unravel the intricacy.L I next set to work to compare the roots of;. the nerves with their distribution; butwhat exceedingly perplexes one in such

endeavours is, the opinion that the nerves are common nerves, just as we say there! is common sensibility. I laboured to show. you lately that there is no such thing as, ! common sensibility; but even the great. authority to which we have clung through-out the whole of this course—JOHN HUN-TER—seems, by the catalogue, to say thatthere is a common sensibility. But Iwould deny that, and say instead, thatthere is a sensibility in the body, whichdiffers in kind and degree, and is evi-dently appointed to regulate or influenceevery part in a due degree. But still thereis a common nerve with common quali-ties, and there is no hope of extricatingourselves out of the difficulty. If we couldbut find an instance where one nerve hasone quality, and another another quality,that would encourage me to persevere. Iobserved in BICHAT’S work this remark-able fact, that in opening a dog and mak-ing a semilunar gash, no pain was mani-fested ; while in irritating the lumbarnerves, pain apparently was felt, and therewas motion. This encourages us to goon, because it implies that sensibility isnot of necessity the effect of nervousmatter, but the nerves may have different

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endowments. Then comes the question,

master, and the account he gave of it; I

can this be a common nerve? It is im- mean ALEXANDER MONR o ;’you will seepossible to contradict what is universally it in his beautiful work on the nervousbelieved. The nerve of the arm or a system. " Here are the muscles of thenerve of the body has a common quality. face," he said; " here are two nerves go-The whole profession cannot be mistaken ing to those muscles, and for this purpose ;in this. Have the nerves roots ? Has Nature is more provident of the face thannerve a common quality, or distinct qua- of other parts, and see here are two nerveslities, because it has distinct roots ? Are going to the same part, lest one should bethe distinct qualities the result of those cut off and life altogether lost; that is toroots having each a different qualification say, if they went together, or there wasor endowment ? If this idea once enter only one nerve, life would be cut off, butthe mind of the anatomist, he remembers in order that that may not take place,"full well that every several nerve has two he says, " the nerves come by differentroots, two classes of roots; not individual foramina, and by different roots to thefibres, but two classes of fibres, running same part." You will not wonder thatlongitudinally, arising in a line, and distinct this was an unsatisfactory view. At allin the manner and place of rising; distinct events, here was a field for observation,in structure ; one with a ganglion and for here are nerves continuing to run byone without. When this fact strikes the a different course, and joining only in theirmind, one naturally says,-It is a pity but fibres; and, after years of labour uponwhat one could ascertain that these roots the anatomy of the nerves, you can con-have different qualities, ceive the pleasure of finding the results

As, then, I was careful enough to make obtained from operating and experi-experiments upon the living animal, and menting. Here is a drawing, in whichcould bring nothing to light, I supposed you see one nerve coming out, whichthat one of the roots was for sensation and I shall fully describe by-and-by, andthe other for motion; that if I touched the there is another. It was pleasing toroot of sensation, the animal would expe- find, that on cutting the seventh pair, allrience pain ; that if I touched the root of motion was stopped, and that on cuttingmotion, no pain would be felt; I therefore the fifth, all sensibility was destroyed,took the less cruel method of destroying while motion remained. Again, then,life, as regards sensibility and pain, and you see it was made clear to demon-then opening the spinal marrow, and as- stration, not merely to such a demon-

certaining what took place on touching stration as a minute anatomist couldwith the point of a needle first one class follow, but obvious to all who possessedof nerves, and then the other. I did so, reason, that the nerves had different qua-and found, on touching the posterior roots lities, and that these resulted from theof a nerve, that no motion took place in nature of their origin,-not their distribu-any part of the body, but upon penetrat- tion, not their structure, but their relationing deeper, and cutting the anterior roots, I to the centre of the nervous system.motion was produced, and the motion was But still, with all this, what is the mean-produced as regularly as the needle went ing of the intricacy ? For supposing thatdown touching the different anterior roots, we were to trace out these nerves, and tojust as distinct as the motion produced by find that they go off with great regularitytouching the keys of a harpsichord. On from the brain and spine to every part oftouching the motory roots no effect is the body, with a double function-at allproduced, and what is wanting is the events, with a double distribution-and,knowledge of the simple fact, that the therefore, were common nerves with com-nerves are appropriated to different pur- mon qualities, it would appear that theposes. Anatomy supplies all the rest, and whole nervous system ought to be verywhen once you are in possession of this simple, because the two qualities go outfact, and you come to understand that together, and the nerves are common.

sensibility and motion are not necessary Then what is the meaning of the intri-consequences of nervous matter, you turn cacy? Recollect the premises ; remem-back to the arrangement of the nerves, to ber what I stated to you before,-thatsee under this new intelligence of their the power of the muscles does not

property what anatomy will do. proceed in one uniform course from theIt was after arranging all this, and ob- sensorium, the moving instrument, nor

serving it, that at last I thought of a new that every sensation experienced in themfield of inquiry, not at the roots, but in the goes directly back to the sensorium, butdistribution of the nerves. Now if this that a number of combinations, or actingwere to enter your minds as anatomists, parts, are associated in the simplest act ofwould you begin to make experiments? I volition. We have further to remark,well recollect the old experiment of my also, that, in many instances, these mus.

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cles, instead of being directly subject to which, it -is quite clear, must be thevolition, are, purposely, and for benevolent sources of motion. Now there is a sourcepurposes, withdrawn from its influence, of motion in each division; each ring hasand adapted to their particular functions a little brain ; each ring has a little divi-independently of it. How? Certainly by sion of nerve,going from it. Here theremeans of nerves, by the relation and con- is something like symmetry ? And why?nexion of nerves; and we shall find, that Each division possesses its little ganglion,in proportion to the intricacy of the rela- and from each ganglion there go off nervestion of muscles to their several functions, to move the numerous muscles, but noso is the complication of the nerves sup- one part can move by itself; there is a

plying them. relation or union established between allThere is another mode of proceeding in the moving parts.

the investigation of this subject, and that In the lobster you see this more perfectis by tracing back our steps, and observing still. The plan of the nervous system isthat the nervous system is accommodated obvious. There is a series of ganglia ato the variety of action which we have little raised; there are distinct series ofalready noticed. Take the mollusca, and eminences, with nerves going from them,you will observe that the nerves are very having one line of connexion runningsimple in them. Now here is an animal through the whole, and imparting com-possessing both senstttion and motion, mon sensibility to the animal-if I maybut without symmetry in its capsule. It now use the words in that sense-andis an oyster. Here is the section of a mus- common motion,-a concatenized motion,cle which is an adductor, and which closes a combined motion.the shell, and here is a nerve going to the Now in these simpler animals or lowermuscle, combining the fibres of the mus- animals, corresponding with their sim-cle together, and here is a point represent- plicity and regularity of form, there is aing a little mass of nervous matter called line of nervous matter connected witha ganglion, and which is the source of each ganglion, and in the higher animalsmotion in the muscle. Then we find a there is the same, only that it is obscurednerve going through the body and ano- by other organs of motion, other centresther ganglion, another nerve belonging to of sensation, and other more intricateanother muscle, which also is designed to branches.close the shell. Then, again, we find a Now if we take a creature lower in thenerve which exhibits no regularity, run- scale than these, the earth-worm, and di-ning up the animal. Here all is irre- vide it, the posterior portion will remaingularity; you see nothing that you writhing and twisting, but there is no as-can call a system. But you have ar- sociated action between the parts. Therived at this knowledge, that where a anterior part will move away. Labouringfaculty is given to a part, that faculty is under the impression of pain in the pos-associated with a certain portion of ner- terior part, it will make its escape. Thusvous matter, and power diverges from it. in the lowest of these animals you find,If, again, you take the star-fish, for ex- that small as the anterior ganglion is, yetample, which belongs altogether to an- it seems to be the superior. It is thatother class of animals, something like which gives animation and consent to allsymmetry will be found in it, but the ex- the others. There, however, the anterioristence of symmetry will not explain what ganglion is acquiring a new property;is intricate in the nervous system of the new muscles are added to it, new nerveshigher animals. You have the mouth, are given forth, and traced out to the newthe ossophagus, the circulating blood, and organs of sense. There is not a new sen-the nerves going out to the several parts sibility to touch and pain, but appropriatewhich require motion, and nerves that nerves and ganglia, which ganglia run to-bestow motion and associate the parts gether into a little mass which we musttogether. call a brain.We take, again, the gasteropods. You There is still another very interesting

remember that we spoke of animals as mode of studying this subject. You knowbeing in classes, of animals in the body of that some insects undergo metamorphoses.which a division existed, a sort of cortex, At one period of their existence they area firm integument, a firmness necessary hermaphrodites, and at another periodto their motion and protection. But if they possess new organs and parts, wingsthe animal consisted of one regular homo- and new muscles. If we are right, then,geneous body, it could not move, and in supposing that the nervous system willtherefore it is divided and articulated in, always bear a relation to the parts to beand surrounded by, an external skeleton, moved, and to the variety of organs pos-the muscles being inserted into different sessed, we have here an interesting occa-segments, or circles, or annular parts, sioa of witnessing that fact. The best

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opportunity of doing so is to be found in nerve was exceedingly small in the root,the change which takes place in the scara- and that in this respect it was obviouslybæus nasicornis. When that animal has distinct from the other nerves. The ques-undergone its metamorphosis, when at tion arose whether it was going up, or,last the wings are expanded, and the rather, coming down, and then the expe-muscles of the wing become active, new riment was made of cutting the sympa-nerves are distributed in that direction, thetic in the neck; and it was conceived,and the very remarkable fact is observe- in some minds, to be conclusive, that theble with your glass, that the nerves which! effect of the division was inflammation ofled to the old muscles of the feet are with- the eye. By-and-by, however, when thedrawn, and disappear altogether, and now whole came to be fairly dissected, wethere seems to be developed, coming into were, as anatomists, relieved from the la-existence, as it were, altogether a new hour of trying to recollect the different re-class of nerves, with fresh intricacies, for lations of the sympathetic, because it camethe muscles moving the wings do not ex- out that its relations were universal. Athibit the regularity of form which distin- that time, too, anatomists were exceed-

guishes the muscles of the feet. Here, ingly curious about the phenomena de-then, is an instance of the whole nervous pendent on its connexion with the fifth andsystem changing its parts, and becoming the portio dura,-the seventh, and so forth.curiously adapted to the new power re- Yet it was obvious that it had as large aquired for moving. connexion with the nerves that went toWe should now attend to the apparent the arm as with those of the head, and it

resemblance in the human body to the line was quite as obvious that it continued toof nerves in the lower animals. the pelvis, and did not terminate there,

In the preparation before me, you see but threw out fibres to the anterior cruralthe sympathetic nerve running its whole nerve, and went down to the extremitiescourse, and you would almost fall into the of the toes. It is plainly, then, an uni-same opinion which others have enter- versal nerve, a nerve extending all overtained, that the sympathetic nerve is the the body, and further remarkable in pos-ganglionic nerve, as it is called, of the sessing no sensibility. It was left forlower animals. Strange it is that this the physiologist to conceive that it was

opinion should be supported by such an the nerve which least communicated withauthority as BICHAT, because he himself the mind, if at all connected therewith,has taught us differently; he has taught or with the sensorium; that it was theus that when the ganglion of the sympa- nerve which united certain parts of thethetic nerve was touched, no irritation body into one ; that it was performing allwas produced that was at all propor- those secret operations of the economytionate to touching one of the other gan- which you know can be directed withoutglions, thus implying that the sympathetic the interference of the mind, such as di-nerve does not possess the quality of re- gestion, assimilation, circulation, and allceiving and conveying impressions, or of the functions which are necessary to theproducing impressions by means of other continuance of life; and there seems, evennerves. What, then, is obvious here? at this time of day, no reason to contestWhy, that this nerve is known only by its that conclusion.negative qualities. It does not move But looking thus at the sympatheticparts, and it creates no sensation. How nerve, we are left to account, as it were,many demonstrations, I ask, were given for all its relations. Although it has ob-of these nerves in former times ? I re- tained the character of accounting for allmember well that I was taught to demon- the sympathies of the body, it really doesstrate the sympathetic nerve, beginning not account for one of them. These de-with a minute dissection of the bones at pend altogether on other relations.the base of the skull, marking its con- Returning then to the spinal nerves,nexion, marking, after a day’s laborious and what is seen upon opening the spinaldissection, its connexion with the sixth canal, and observing the spinal chord andand the second division of the fifth, tra- the nerves which proceed from it withcing down the nerve along the artery, such great regularity, we notice that eachmarking its coming from the jaw and nerve has two distinct roots; one setcommunicating with the ninth and sympa- coming from one column of the spinalthetic, with the, eighth and the cervi- marrow, and the other coming from thecal nerves,-observing its superior gan- other column. Through the relation ofglion in the neck, the lower ganglion, and these to the sensorium a man experiencesthen the succession of ganglia running all the innuences of external agents, anddown to the body. has the various capacities of motion; thatBut there arose no thought in the mind is to say, by their means he is subjected

of the physiologist at that time that this to the different influences which animate

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him, and on which depend all the powersby which he moves and becomes an agent.This is enough to know until you recollectthat these powers must be maintained bythe operations of the animal economy, andfor which operations you have not yetaccounted.

Presenting the subject to ourselves inthis manner, we say that man is thus con-stituted with a capability of receiving andacting upon impressions, of locomotion,and of every sort of .agency ; yet with allthis he is but half made up, for he cannotbreathe. Now suppose all the muscles ofrespiration had to be put into action bythe effort of the will,-that man had to sethimself to work those muscles; why youknow full well that all the actions of vo-lition are brought forth only very slowly,and by means of experience, until at lastthey become perfect. Can you say thenthat the function of respiration should beperformed after the same manner that hemoves a limb ? No. That mode requirestime, experience, and improvement, andnature, therefore, has provided differentlyfor breathing. She has established an in.stinctive feeling, a new sense of motion,different sets of nerves for the performanceof that function, and these nerves, underthe influence of instinctive’ action, begin,the moment that life commences, to per-form the purposes required of them, andwithout them it is quite clear that lifecould not continue.

This, then, introduces us to the subjectof the respiratory nerves, and a verycurious and interesting but difficult in-

quiry here meets us :-Is there any pointin the nervous system which seems, more

. than another, to be the centre from whichthe nervous power diverges to thoseseveral muscles which are necessarily as-sociated in the act of drawing breath ?

Let us here draw on our recollection.If an animal be struck at one point of thehead, it dies in an instant; it never drawsbreath again. The blow produces no pain,no struggling; but the act of respirationceases, and such is the condition of theanimal if that act be cut off at once. Butif the spinal chord be divided at a certaindistance below that point, motion andsensibility are cut off, while respirationcontinues. Even if the spine be fractured,and the column torn across below the ori-gin of the phrenic, the man lies dead andpowerless in his body and limbs, but theact of respiration is still perfect, becausethe nerves going off to the face, nostrils,mouth, and lips, to the sterno-cleido mas-toideus, the muscles of the shoulder, andthe muscles of the outside of the chest,are untouched at their roots, and continue

their operation, though sense and motionbe gone in the rest of the body.In experiments in which the brain is

cut off slice after slice,-though the seat ofvoluntary power is removed, the centre towhich every sensation is referred is takenaway, the source of all voluntary motionis destroyed,-yet the act of respirationcontinues. Proceed a little farther, andinterfere with the source of the nerves,when, instantly, the respiration stops.This brings us to the roots of the nerves.We are thus like children playing at hideand seek; we know something about it,but not all. We know that we cannot befar from the part in which the source ofmotion is secreted. We have found thatthough a given part be destroyed, motioncontinues ; if the part above be destroyed,it continues ; but if the intervening por-tion be destroyed, it ceases in an instant.We may next draw an illustration from

an acephalous child. If a child be bornwithout a medulla oblongata, it is deadbom ; but if it be born without a brainand have a medulla oblongata, it breathesand lives for some time. Thus the motionof respiration does not depend upon thebrain; certainly it does not depend uponthe spinal marrow; but we are near thepoint on which it does depend, and wefind now that the nerve which goes downto the pharynx, the larynx, the trachea,the heart, the lungs, and the stomach,comes from this very point, and that thosenerves which go to the external parts ofthe body, and which move in the act ofrespiration, come from the same place.Does it not appear, then, that the ex-

periments, or, as I may say, the analogieswe draw,-all that we can deduce by theaid of reason, corresponds with the factsdisclosed by the anatomy of the body ?

Still, however, we find an extraordinarydegree of complexity existing. The nerveson one side of the neck are complex, evenin the lower animals, and they are ex-ceedingly complex in the human body.What is the meaning of this complexity?Even upon the supposition that the nervesproceed from a common centre,-thatnerves of one class go forth to producemotion and sensibility, and another toeffect respiration,-how can we account forall this irregularity, until we rememberthat the grand function of respiration, ofdecarbonization of the blood,-the grandfunction which is necessary to be per-formed in order to perpetuate the otherdifferent functions of the living frame, isused for a different purpose than its cha-racteristic one ? I formerly had occasionto state that a variety of purposes wasanswered by one agent or point, and anopportunity is here given in the act of

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respiration to show the performance,by the agents of respiration, of other

functions, functions which are most im-portant to the mind,-for instance, speech,without which philosophers acknowledgethere can be no high cultivation of themind, for speech is the very instrument of ,Ithought. ,

Well, then, only consider how many partsmust be united and related one to another,before a man can utter even a simplesound, and how many more before out ofsimple sounds he can form an articulatelanguage, and then you will not be sur-prised at the intricacy of the nerves of theneck, but you will proceed with increasedanxiety to dissect each particular branchof them, ir. order to observe their variousfunctions and the high and importantresults of each individual part. But thereis a variety of proofs of the distinctnature of these common nerves-I meanthe system of nerves-and one is the dis-tinction which exists amongst those ofwhich I spoke as separate nerves. Thereis nothing so remarkable as this, that thedeath of one nerve will occur before thedeath of another-that when all sensibilityis gone, when all capacity of receivingimpressions of any kind is, as it were,dead, the act of respiration still remains

perfect. We may say, in fact, in oneword, that these nerves are the last todie.There is one thing more upon which I

wish you to reflect. It is a circumstanceof high interest, and of much importance,I think, in pathology. You infer, and weare all apt to infer, perhaps with perfectcorrectness, that the eighth pair of nerves,and the muscles which they excite, are

under the influence of the condition ofthe chest, and, undoubtedly, when werecollect the distribution of the eighthpair, such must appear to be the fact.Well, then, mark this, that when you havedivided the spinal marrow (and throughthe spinal marrow there is no connexionwith the lungs), when you have dividedthe eighth pair of’nerves in the animal-the horse or the ass (and you rememberthat in those animals dividing the eighthpair is dividing the sympathetic)-thereremains no connexion between the lungs,the heart, and the external respiratoryparts. Yet they continue to act. They donot act as the limb of an animal would act ifit were rapidly separated from the body anda galvanic influence were applied to it.Here there is a combination among allthe muscles, and there is proof that thecombination is in the body. What is thenature of the influence which the brain orthe sensorium holds over them it is noteasy to say; but we have proof that when

! the head is removed these muscles act,-are concentrated together,-and the unionof these muscles, therefore, must he in thebody.

Now, when we cut off the body, by thedivision of the spinal marrow, and havecut off the connexion with the lungs bythe division of the eighth pair, the act ofrespiration still goes on, and from this Iwould infer that there is a source of mo-tion in the nerve of respiration, or in themedulla oblongata, independent of the

lungs, and independent altogether of thestate of the parts within. The point,therefore, which I conceive it importantfor you to observe is this,whether ornot the morbid conditions of the functionof respiration,-whether some of thosesudden deaths in which a breath is notdrawn again, where the features are leftundisturbed, where there is not the least

pain,-are at all to be accounted for bysupposing them to be the result of an

affection of the centre of the nervous sys-tem, as regards the great function of re-spiration, rather than an affection of theheart or lungs ?

It is a subject of difficulty, but you willbe excited to its examination by its im.portance.

LECTURE XV.

(CONCLUDING LECTURE.)

EPITOME OF THE NERVOUS SYSTEM.

GENTLEMEN,ńWere I to follow my owninclinations, I should rather wish to dwellupon the eighth pair, because undoubt-edly they present much that is novel.There is a great deal still to be deter-mined regarding its origin, distribution,and functions, but the present course isso nearly at a close, that I must advanceat once to a subject on which there isno variety of opinion, at least regardingfacts, and make a comparison between thenerves going off from the encephalon, andthose from the spinal marrow.Even this would serve me to bring to

your recollection, that on looking at thebase of the brain, a remarkable differ-ence is discernible between the nervesgoing off from that portion of the nervoussystem, and those which issue from thespinal marrow. In the spinal marrow yousee each nerve with a regular double root,and one ganglion at one of the roots, and,as we have hitherto supposed, those arecombined together and form what willstill be, in a limited sense, a compound orcommon nerve. But when we look at

those nerves Nvli*.ch go off from the brain,