Of the Nerves in general.

1. BY the Assistance of Injections and Microscopes wonderful Plexuses of Blood-vessels are discovered to go from the Pia Mater into the Cortex, cincri­tious, or ashy-coloured Part of the Cerebrum, Cerebellum and spinal Marrow, whereas we can only see longitudinal Vessels, without nu­merous Ramifications or reticular Plexuses, in the white medullary Substance of these Parts.

2. The Continuity of the Cortex with the Medulla of the Encephalon and spinal Marrow is observable with the naked Eye, and is more distinctly seen with the Assistance of a Micro­scope.

3. In dissecting the Brain and Cerebellum, we see the small Beginnings of the Medulla proceeding from the Cortex, and can trace its gradual Increase by the Addition of more Me­dulla coming from the Cortex.

4. Both Cortex and Medulla are very succu­lent; for being exposed to the Air to dry, they lose more of their Weight than most other Parts of the Body do.

5. In several Places we can observe the Me­dulla to be composed of Fibres laid at each o­ther's Sides.

6. The medullary Substance is all employed in forming the white fibrous Cords, which have now the Name of Nerves appropriated to them. Within the Skull we see the Nerves to be the medullary substance continued, and the medulla spinalis is all employed in forming Nerves.

7. The common Opinion concerning the Rise of the Nerves, founded on a superficial Inspection of those Parts, is, that the Nerves are propagated from the same Side of the En­cephalon at which they go out. But it having been remarked, after a more strict Enquiry, and preparing the Parts by Maceration in Wa­ter, that the medullary Fibres decussate or cross each other in some Parts of the Medulla; as for Example, at the Corpus annulare, and Beginning of the Medulla spinalis: And practi­cal Observators having related several Ex­amples of People, whose Brain was hurt on one Side, while the morbid Symptom, Palsy, appeared on the other Side of the Body, of which I have seen two Instances; and Experi­ments made on Brutes having confirmed these [Page 3]Observations, it has been thought, that the Nerves had their Rise from the Side of the En­cephalon, opposite to their Egress from the Skull. It may however still be said, that this last Opinion is not fully demonstrated, because a Decussation in some few Parts is not a Proof that it obtains universally; and if there are Ex­amples of Palsy of the Side opposite to where the Lesion of the Brain was, there are also o­thers, where the Injury done to the Brain and the Palsy were both on the same Side.

8. The Nerves are composed of a great ma­ny Threads lying parallel, where they come out from the Medulla.

This fibrous Texture is evident at the Ori­gin of most of the Nerves within the Skull, and in the Cauda equine of the Medulla spinalis, we can divide them into such small Threads, that a very quick-sighted Eye can scarce per­ceive them; but these Threads, when looked at with a Microscope, appear each to be com­posed of a great Number of smaller Threads.

9. How small one of these Fibrils of the Nerves is we know not, but when we consi­der that every, even the most minute Part of the Body is sensible, and that this must depend on the Nerves (which all conjoined would not make a Cord of an Inch Diameter) being divided into Branches or Filaments to be dis­persed through all these minute Parts, we must be convinced that the nervous Fibrils are very small. From the Examination of the mini­mum visibile it is demonstrated, that each Fibre in the Retina of the Eye, or expanded optick Nerve, cannot exceed the Size of the 32400 Part of a Hair.

10. The medullary Substance, of which the nervous Fibrils are composed, is very ten­der, and would not be able to resist the com­mon Force of the circulating Fluids, and other such Forces to which the Nerves are exposed within the Bones, were not the Pia Mater and Tunica Arachnoides continued upon them. The former giving them Firmness and Strength, and the latter furnishing a cellular Coat to connect the Threads of the Nerves, to let them ly soft and mo [...]st, and to support the Vessels which go with them.

It is this cellular Substance that is distended with Air when it is blown through a Blow­pipe thrust into a Nerve, and that makes a Nerve appear all spungy, after being distended with Air till it dries, the proper nervous Fibrils shriveling so in drying as they scarce can be observed.

11. These Coats, § 10. would not make the Nerves strong enough to bear the stretching and Pressure they are exposed to in their Course to the different Parts of the Body; and therefore as the Nerves are going out at the Holes in the Cranium and Spine, the Dura Mater is closely wrapt round them, to collect their disgregated Fibres into tense firm Cords, and that the stretching they may be exposed to may have no Effect to hurt them where they are not strength­ned thus by the Dura Mater; this strong Membrane is firmly fixed to the Sides of the Holes in the Bones through which they pass.

12. The nervous Cords thus composed of nervous Fibrils, cellular Coat, Pia and Dura Mater, have such numerous Blood-vessels be­stowed on them, that after their Arteries only [Page 5]are injected, the whole Cord can be tinged of the Colour of the injected Liquor; and if the Injection is pushed too violently, the cellular Substance of the Nerves comes to be distended with it.

13. A nervous Cord, such as has been just now described, § 12. has very little Elasticity, compared with other Parts of the Body. When cut out of the Body, it does not become obser­vably shorter, while the Blood-vessels contract three Eighths of their Length.

14. In the Course which the Nerves have to the several Parts of the Body, they are gene­rally lodged in a cellular or fatty substance, and run in the Interstices of the Muscles and other active Organs, that so they might be little exposed to the Pressure which these Parts would make upon them, and might be defen­ded from any bad Effects which such Pressure might otherwise produce.

15. The larger Cords of the Nerves divide into Branches in their Distribut on to the dif­ferent Parts; the Branches being smaller than the Trunk from which they come, and making generally an acute angle where they separate.

16. In several Places different Nerves unite into one Cord, which is commonly larger than any of the Nerves which form [...]t.

17. Several Nerves, particularly those which are distributed to the [...]ow [...]ls, sudden­ly form a hard Knot. considerably larger than all the Nerves of which it is made. These Knots were called Corpora olivaria, and are now generally named Ganglions.

18. The Ganglions have much thicker Coats and larger, more numerous Blood-vessels than [Page 6]the Nerves, so that they appear redder and more muscular. On dissecting the Ganglions, Fibres are seen running longitudinally in their Axes, and other Fibres are derived from their Sides in an oblique direction to the longitudi­nal ones.

19. The Nerves which go out from the Ganglions are no way remarkably different from other Nerves.

20. The Nerves that are sent to our Organs of the Senses lose there their firm Coats, and terminate in a pulpy Substance. The optick Nerves are expanded into the soft tender Webs the Retinae; the auditory Nerve has scarce the Consistence of Mucus in the Vestibulum, Co­chlea and semicircular Canals of each Ear; the Papillae of the Nose, Tongue and Skin are ve­ry soft.

21. The Nerves of Muscles can likewise be traced till they lose their Coats and become very soft, from which, and what we observed of the sensatory Nerves, § 20. there is Reason to conclude, that the muscular Nerves are al­so pulpy at their Terminations, which we can­not indeed prosecute by Dissection.

22. It would seem necessary that the Extremities of the Nerves should continue in this soft flexible State, (§ 20, 21.) in order to per­form their Functions right: For in proportion as Parts become rigid and firm by Age, or any other Cause, they lose of their Sensibility, and the Motions are more difficultly performed.

23. Tho' the Fibres in a nervous Cord are firmly connected, and frequently different Nerves join into one Trunk, or into the same Ganglion, yet the Sensation of each Part of the [Page 7]Body is so very distinct; and we have so much the Power of moving the Muscles separate­ly, that, if the Nerves are principal Agents in these two Functions, which I shall endeavour to prove they are, we have Reason to believe that there is no Union, Confusion or immedi­ate Communication of the proper nervous Fi­brils, but that each Fibre remains distinct from its Origin to its Termination.

24. Changes produced any way upon the Coats of the Nerves cannot however miss to affect the nervous Fibrils. The cellular Sub­stance may be too full of Liquor or may not supply enough; the Liquor may not be of a due Consistence, or it may be preternaturally obstructed and collected. The Pia Mater may be too tense or too lax, as may also the Dura Mater; their Vessels may be obstructed; their proper Nerves may be violently irritated or lose their Power of acting; and a great many other such Changes may happen which will not only occasion Disorders in particular Nerves, but may cause the Sympathy so fre­quently Observed among the Nerves, which is so necessary to be attentively regarded in a great many Diseases in order to discover their true State and Nature, without the Knowledge of which we must commit very dangerous Mis­takes in the Practice of Physick and Surgery.

25. Many Experiments and Observations concur in proving, that when Nerves are com­pressed, cut, or any other way destroyed, the Parts served by such Nerves farther from the Head or Spine than where the injuring Cause has been applied have their Sensations, Moti­ous and Nourishment weakned or lost, while [Page 8]no such Effects are seen in the Parts nearer to the Origins of those Nerves; and in such Experiments where the Cause impeding the Nerves to exert themselves could be removed, and the Structure of the Nerves not injured; as for Example, when a Ligature made upon a Nerve and stopping its Influence has been taken away, the Motion and Sensation of the Parts soon were restored. From which it would appear that the Nerves are principal Instruments in our Sensations, Motions and Nourishment; and that this Influence of the Nerves is not inherent in them without the Communication between these Cords, and their Origin is preserved.

It will be no Objection to this Conclusion, that sometimes, upon cutting a Nerve, the Ef­fects above-mentioned have been felt for a short Time, but afterwards the Person was sensible of no Numness or Immobility; for wherever this is said to have happened, the cut Nerve was only one of several which were sent to the Member, the want of whose Influence would be felt no longer than till the Habit was acquired of performing the Functi­ons casily by the other Nerves.

It is of no greater Weight as an Objection, that when a Ligature is drawn very hard upon a Nerve, the Nerve never again recovers its Influence upon the Parts it is distributed to be­yond the Ligature, but is of as little Effect as if it had, been cut thro'; which is to say, that its Texture has been alter'd beyond Recovery. The same Thing is to be seen by tying a Thread tight round a tender Twig of any ve­getable, it decays.

26. Experiments and Observations shew too, that when Parts of the Encephalon or Me­dulla spinalis have been irritated, compressed or destroyed, the Parts of the Body, whose Nerves had their Origin from such affected Parts of the Encephalon or Medulla spinalis, became convulsed, paralytick, insensible or wasted; and in such Cases where the injuring Cause could be removed from the Origin of the Nerves, the morbid Symptoms observed in the Parts to which these Nerves were dis­tributed, went off upon the Removal of that Cause. From which it is thought reasonable to conclude, that the Nerves must not only have a Communication with their Origin, but that the Influence they have upon the Parts they are distributed to, depends on the Influence which they derive from the Medulla Encephali and spinalis.

27. Tho' the Medulla spinalis has its own Vessels and cineritious Substance which assists to form its Medulla, yet a very large Share of the Medullary Substance within the Spine is derived from the Encephalon, whose Medulla oblongata descends from the Head, and the In­fluence of the Medulla spinallis on its Nerves depends in a great Measure on this Medulla oblongata of the Head. Hence an Injury done to any Part of the Medulla spinalis immediate­ly affects all the Parts whose Nerves have their Origin below where the injuring Cause is applied to the Spinal Marrow. A Luxa­tion of a Vertebra in the Loins makes the low­er Extremities soon paralytick; a transverse Section of the Medulla at the first Vertebra of the Neck soon puts an End to Life.

28. If such Causes produce constantly such Effects (§ 25, 26, 27,) in us and other Creatures living in nearly the same Circum­stances as we do, the Conclusions already made will be good, notwithstanding Exam­ples of Children and other Creatures being born without Brains or Medulla spinalis; or notwithstanding the Brains of adult Creatures being much changed in their Texture by Dis­eases, and notwithstanding the Experiments of cutting off the Heads of Tortoises, and some o­ther Animals which continued to move about a considerable Time after their Heads were off. We may be ignorant of the particular Circumstances requisite or necessary to the Be­ing or Wellbeing of this or that particular Creature, and we may be unable to account for a great many Phaenomena; but we must be­lieve our Eyes in the Examination of Facts, and if we see constantly such Consequences from such Actions, we cannot but conclude the one to be the Cause, and the other the Ef­fect. It would be as unjust to deny the Con­clusions made in the three preceeding Ar­ticles, because of the seemingly preternatural Phaenomena mentioned in the Beginning of this, as it would be to deny the Necessity of the Circulation of the Blood in us and Qua­drupeds, because a Frog can jump about or a Tortoise can walk long after all the Bowels of its Thorax and Abdomen are taken out, or be­cause the different Parts of a Worm crawl af­ter it has heen cut into a great many Pieces. It is therefore almost universally agreed that the Nerves are principal Instruments in our Sensations, Motion and Nourishment, and [Page 11]that the Influence which they have is commu­nicated from their Origin, the Encephalon and Medulla spinallis; but Authors are far from a­greeing about the Manner in which this In­fluence is communicated, or in what Way Nerves act to produce these Effects.

29. Some alledge that the nervous Fibres are all solid Cords acting by Elasticity or Vibra­tion. Others affirm that those Fibres are small Pipes conveying Liquors, by means of which all their Effects are produced.

30. The Gentlemen, who think the nervous Fibres solid, raise several Objections to the o­ther Doctrine, which I shall consider after­wards, and endeavour to shew the Fitness of their own Doctrine to account for the Effects commonly observed to be produced by the Nerves.

The Objects of the Senses plainly, say they, make Impulses on the Nerves of the proper Organs, which must shake the nervous Fi­brils, and this Vibration must be propagated a­long the whole Cord to its other Extremity or Origin, as happens in other tense Strings; and these Vibrations being differently modified ac­cording to the Difference of the Object, and its different Application, produce the different Ideas we have of Objects.

31. To this Account of the Sensations it is objected, 1st, That Nerves are unfit for Vibra­tions, because their Extremities, where Ob­jects are applied to them, are quite soft and pappy, (§ 20.) and not susceptible of the Vi­brations supposed; and if there could be any little Tremor made here by the Impulse of Ob­jects, it could not be continued along the ner­vous [Page 12]Cord, because the cellular Substance by which each particular Fibre is connected to the neighbouring ones, (§ 10.) and the fatty Substance in which the nervous Cord is im­mersed (§ 14) would soon stifle any such vi­bratory Motion.

The 2 d Objection to this Doctrine is, that, supposing the Nerves capable of Vibrations by the Impressions of Objects, these Vibrations would not answer the Design. For if what we know of other vibrating Strings, to wit, that their Tone remains the same, unless their Texture, Length or Tension is altered, and that different Substances striking them do no more than make the Sound higher or lower: If these Properties are to be applied to Nerves, then it will follow that the same Nerve would constantly convey the same Idea, with no o­ther Variety than of its being weaker or strong­er, whatever different Objects were applied to it, unless we suppose the Nerve changed in its Texture, Length or Tension each Time a different Object is applied, which, it is pre­sumed, no Body will undertake to prove does happen. But further, if ever such a Variety of Vibrations could be made, our Sensations would notwithstanding be confused and indi­stinct, because the tremulous nervous Fibre being firmly connected, and contiguous to se­veral other Fibres of the same Cord, would necessarily shake them too, by which we should have the Notion of the Object as ap­plied at all the different Parts where the Extre­mities of thes [...] Fibres terminate.

32. In whatever way the Favourers of the Doctrine of solid Nerves please to apply the [Page 13]Elasticity of Nerves to the Contraction of Muscles; their Adversaries insist that Nerves are too weak to resist such Weights as the Muscles sustain, they would surely break, e­specially that they are greatly, if not wholly, deprived of their strong Coats before they come to the Part of the Muscle, they are immedi­ately to act upon (§ 21.) and the Nerves be­ing found to have little or no Elasticity to shorten themselves (§ 12.) shews them alto­gether unfit for such an Office as this of con­tracting Muscles in the way proposed of their acting by Elasticity.

33. As a further Objection against either Motion or Sensation being owing to the E­lasticity of the Nerves, it is said, that if this Doctrine was true, the Sensations would be more acute, and the Contractions of Muscles would be greater and stronger, when the Parts become firmer and more rigid by Age; for then their Elasticity is increased: Whereas on the contrary it appears, (§ 22.) that then the Sensations are blunted, and muscular Con­traction becomes less and weaker.

34. If the Nerves were granted to be elastic, and to communicate a springy Force to all the Parts they are distributed to, they might ap­pear necessary in this View to assist the Appli­cation of the nutritious Particles of the Fluids to the Sides of the Vessels these Particles were to repair; and so far might well enough ac­count for the Share Nerves are thought to have in Nutrition; yet if we cannot make use of Elasticity in the other two Functi­ons of Sensation and Motion, we must also endeavour to find out some other Way the [Page 14]Nerves act in Nutrition, which will be done afterwards.

35. Having thus stated the Reasons for and against the Nerves acting as solid Strings, let us likewise relate the Arguments for Nerves being Pipes, and the Objections to this Do­ctrine.

A great Argument of those who think the Nerves to be Tubes conveying Liquors, is the strong Analogy of the Brain and Nerves to o­ther Glands of the Body and their Excretories, where a manifest Secretion of Liquor is made in the Glands to be conveyed by the Excre­tories, to the proper Places in which it ought to be deposited: They think that the vascular Texture of the Cortex of the Encephalon and Medulla spinalis (§ 1.); the Continuation of the Cortex in forming the medullary Sub­stance (§ 2.3.), the fibrous Texture (§ 5.) and succulent State of this Medulla (§ 4.), and its being wholly employed to form the Nerves (§6.), where the fibrous Texture is evident (§8.); all these Things, say they, conspire to shew such a strong Analogy between these Parts and the other Glands of the Body, as carries a Conviction that there is a Liquor se­creted in the Encephalon and Medulla spinalis, to be sent out by the Nerves to the different Parts of the Body.

36. The following Objections are raised to this Argument in favour of a Liquor convey­ed in the Nerves, from the Analogy of the Glands. 1st, Other Glands, it is said, have their Excretories collected into a few large Pipes, and not continued in such a great Num­ber of separate Pipes, as far as the Places [Page 15]where the Liquors are deposited, which last must be the Case, if the Nerves are the Ex­cretories of the glandular Brain. 2 dly, We see the Cavities and can examine the Liquors in the Excretories of other Glands much smal­ler than the Brain, which cannot be done in the Nerves. 3 dly, If the Nerves were Pipes, they would be so small that the Attraction of their Sides to their Liquors would be so great, that the Liquors could not be moved with the Celerity required to influence our Sensations and Motions, in the quick Manner we see them performed. 4 thly, If the Nerves were Pipes they would be cylindrical ones, and consequently not subject to Diseases, or at least we could have no Comprehension of the Diseases in them.

37. The Answer to the 1st of these Ob­jections is, That there are other Glands where there is a manifest Secretion, and in which the Disposition of the Excretories is in much the same way as in the Encephalon; the Kidneys, for Example, have a reticulated Cortex of Vessels, from which the Eustachian or Bellinian Medulla, consisting of longitudinal Fibres and a few longitudinal Blood Vessels, proceeds; and this Medulla is collected into ten or twelve Papillae, each of which is formed of numer­ous small separate Pipes, which singly dis­charge the Urine into the large membranous Tubes, which united compose the Pelvis. Upon comparing this Texture of the Kidney with what was said of the Encephalon, (§ 1, 2, 3, 4, 5, 6, 8.) the Analogy will be found very strong.

38. In Answer to the 2 d Objection in § 36. [Page 16]it is granted, that Microscopes, Injections, and all the other Arts hitherto employed have not shewn the Cavities of the nervous Fibrils, or the Liquors contained in them; and from what was said (§ 9.) of the smallness of the nervous Fibrils, it is not to be expected that ever they should be seen. But so long as such a Number of little Animals can every Hour be brought to the Framers of this Objection, in which they can as little demonstrate the Vessels or contained Fluids, it will not be al­lowed to be conclusive Reasoning, that be­cause ocular Demonstration cannot be given of Pipes, therefore they do not exist. For if we have any Notion of an Animal, it is its being a Hydraulick Machine, which has Li­quors moving in it as long as it has Life; if therefore such little Animals have Vessels and Liquors which we cannot see, why may not some of the Vessels and Liquors of the hu­man Body be also invisible to us.

To avoid this Answer to the Objection, it is further urged that tho' we might not see the Canals and Liquors of Nerves as they are flowing naturally, yet they ought to discover themselves by the Canals being stretched, or a Nerve's swelling upon being firmly tied; and it might likewise be expected, that how­ever subtile the Liquor of the Nerves is, it might be collected in some Drops at least, when the cut End of a Nerve of a living Animal is kept some Time in the exhausted Receiver of an Air-Pump. It is affirmed, that neither did the tied Nerve swell between the Brain and Ligature, nor was there any Liquor collected in the Receiver of the Air-Pump, from which [Page 17]it is concluded that there is no Liquor in the Nerves.

There is some Difference among those who say they have tried these Experiments, some affirming that in young Animals the Nerve does swell above the Ligature, and that a Li­quor does drill out upon cutting a Nerve. But allowing the Experiments to succeed any way, the Reply to the Inference from them is, that in neither way are they any thing to the Pur­pose; for the swelling of the Nerve after it is tied, or the Efflux of Liquors from its Ex­tremity, will never prove either to be the Ef­fect of the Fluid in the proper nervous Fibrils, so long as they might be occasioned by the Li­quors in the larger Vessels of the cellular Sub­stance of the Nerves; and if these same Ves­sels of the Coats of the Nerves do not dis­cover their Liquors by these Experiments, it is far less to be expected that the much more subtile Nerves should.

39. The 3 d Objection to the Doctrine of the Brain being a Gland, and the Nerves its Ex­cretories, supposes a more rapid Motion ne­cessary in the Fluid of the Nerves, than what most of the Defenders of the nervous Fluid will now allow, and is afterwards to be con­sidered particularly in a more proper Place.

40. The 4 th Objection being, that if Nerves are Excretories of a Gland, they must be cy­lindrical Pipes, in which no Obstructions or Diseases would happen; but since we daily see Diseases in the Nerves, they must there­fore not be such Excretories. The Answer is, That Diseases happen often in the Excretories of other Glands as of the Liver, Kidneys, &c. [Page 18]notwithstanding their cylindrical Form, and their much shorter and less exposed Course. When we consider the very tender Substance of the Brain; the vast Complication of Vessels there; the prodigious Smalness of the Pipes going out from it; the many moving Powers which the Nerves are to undergo the shock of; and the many Chances which the Vessels, Membranes and cellular Substance accom­panying the Nerves have of being disordered, and then affecting the nervous Fibrils, we have very great Reason to be surprized, that these cylindrical Pipes are not much more fre­quently put out of Order by too great or too small a Quantity of Liquors; by too viscid or too thin Fluids; by Liquors consisting of too mild and sluggish Particles, or of too acrid pungent ones; by too great or too little Mo­tion given to the Liquors; by the Diameters of the Pipes being too much straitned, or too much enlarged; and by a great many other Va­rieties of Circumstances which might be sup­posed capable of disturbing the Functions of the Nerves, supposing them to be cylindrical Excretories of the Gland the Brain.

41. The numerous Vessels of the Encepha­lon have brought some of the Gentlemen who defend the Opinion of the Nerves being solid, to acknowledge, that there is a Liquor se­creted in the Brain; but then they will not al­low that this Liquor is sent out by the proper nervous Fibrils, but that it is poured into the cellular Substance in which the Nerves ly, to keep them moist and supple, and therefore fit for exerting their Elasticity, Vibration, &c. [Page 19]by which, in their Opinion, the Effects com­monly ascribed to Nerves are produced.

42. Besides the Objections already men­tioned (§ 31, 32,) against the Nerves acting as elastick Strings, this Opinion has some other Difficulties attending it, that may be urged as Objections to it; such as, there is not one Example in the Body of Liquors secreted in a large Gland being poured into a cellular Su [...]stance, as here supposed; the Liquors in the Cells of the tunica cellularis of other Parts are separated from the little Arteries which are distributed to these Cells.

Further, it can't be well determined, how a Liquor secreted in the Cortex of the Brain should make its Way through the Medulla to come out into the cellular Membranes on the Surface of that Medulla.

Lastly, A very simple Experiment of inje­cting Water by the Artery of any Member, and thereby filling the cellular substance of the Nerves of that Member, shews evidently that the Liquor of the tunica cellularis of the Nerves has the same Fountain as the Liquor in the tunica cellularis has any where else, that is, from the little Arteries dispersed upon it.

43. The Doctrine of a Fluid in the Nerves is not only thus supported by the Analogy of the Brain and Nerves to the other Glands and their Excretories, but those who maintain this Doctrine mention an Experiment which they think directly probative of a Fluid in the Nerves; it is this. After opening the Tho­rax of a living Dog, catch hold of and press one or both the phrenic Nerves with the Fingers, the Diaphragm immediately ceases [Page 20]to contract; then let go the hold of the Nerves, and the Muscle acts again: Pinch a second time the Nerve or Nerves some way above the Diaphragm, this Muscle again ceases to act: Keep firm the Hold of the Nerve, and with the Fingers of the other Hand strip it down from the gripping Fingers towards the Diaphragm, and the Muscle is made to contract; and for three or four such Stripings its Action follows or obeys the Motion of the Fingers which strip it down; then it becomes disobedient, and will contract no more, strip as you will, un­less the Fingers gripping or pinching the Nerve let go their Hold, or are removed higher up upon the Nerve, when the Muscle may again be made to contract by stripping the Nerve down towards it. This Experiment I have done with the Success here mentioned. Let any one try if he can imagine any other reason­able Account of these Appearances, than that the gripping Fingers stopt the Course of a Fluid in the Nerve; that what of this Fluid was thus made to stagnate in the Part of the Nerve between the gripping Fingers and Diaphragm, was forced down into that Muscle by the Pres­sure of the Fingers which stripped the Nerve down; and when ever this stagnating Fluid was pressed all away by several Repetitions of stripping the Nerve, the Muscle being sup­plied with no more Fluid contracted no more, till upon removing the Fingers which had hold of the Nerve, a new Supply of Liquor was brought from the Brain, or from the Part of the Nerve that had not yet been grip'd or strip­ped; and when ever this Liquor could make its Way down to the Muscle, or was forced [Page 21]down to it, the Muscle immediately began to renew its contractile Motions.

44. Some Gentlemen convinced of the Rea­sonableness of the Secretion of a Liquor in the Brain to be sent out by the Nerves, but not comprehending how a Fluid could have such a rapid retrograde Motion as they imagined was necessary for conveying the Impressions of Ob­jects made on the Extremities of Nerves to the Sensorium, supposed two Sorts of Nerves, one that conveyed a Liquor for muscular Mo­tion and Nutrition; the other composed of so­lid Nerves, that were to serve for the Organs of the Senses, to convey the Vibrations com­municated from Objects to the Sensorium.

45. The Objections mentioned (§ 31.) a­gainst the sensatory Nerves acting by Vibra­tions take place here: And further, there is nothing in the Texture either of the Brain or Nerves, which gives any Reason to think, that the Nerves are differently formed; on the con­trary, the Structure is every where similar, and often Branches of the same Nerve serve both for Sensation and Motion. What occasioned justly a Prejudice against the Scheme of our Sensations depending on a Fluid in the Nerves, to wit, the rapid Refluxes supposed in the sensi­tive Nerves, is an Opinion now deserted ge­nerally by the Defenders of the nervous Fluid, for Reasons to be given in a little, tho' their Opponents are still willing to palm it on them, whereby they may have a better Handle against the general Doctrine of the nervous Fluid.

46. This same rapid Refluxat was too, which gave Rise to another Division of the Nerves into arterious or effluent, and venous or reflu­ent. [Page 22]It was said, that muscular Motion and Nutrition depended on the arterious Nerves, and that the Sensations depended on an accele­rated Motion of the nervous Fluid towards the Brain, by the Impressions which the Ob­jects of the Senses make upon the venous Nerves. By this Supposition the Absurdity of rapid Fluxes and Refluxes in the same Canal was prevented, and an Advantage was thought to be gained by it, of saving too great a W [...]ste of the Fluid of the Nerves, which otherwise the Encephalon and Medulla spinalis could not supply in sufficient Quantity to answer all the Exigencies of Life.

47. To this Opinion (§ 46.) it has been objected, 1. That there is no Example in the Body of a secreted Liquor being returned im­mediately and unmixed to the Gland by which it was originally separated from the Mass of Blood, which would be the Case were there venous Nerves. 2 dly, There is no Occasion for saving the Fluid of the Nerves in the Way proposed, the Organs for secreting that Fluid being large enough to supply all that is neces­sary o [...] it in the common Functions of Life. 3 dly, If the Fluid of the Nerves was to be thus kept in a perp [...]tual Circulation, it would soon become too acrid for continuing with safety in such sensible tender Vessels as the Brain and Nerves are composed of. 4 thly, This Hypo­thesis will not answer the Design for which it was proposed. For tho' the momentary Ap­plication of an Object might cause an Accele­ration in the Fluid of venous Nerves, yet if the Object was kept applied to the Nerves, it would stop their Fluid, so that it could not go [Page 23]forward to the Brain; and therefore, according to this Doctrine, we should be sensible of no Objects, except those whose Application to the Organs of the Senses was momentary.

48. Let us now suppose it probable, that the Encephalon and Medulla spinalis secern a Li­quor from the Blood which is sent into all the Nerves, and that by the Means of this Liquor the Nerves perform the Offices commonly as­signed to them, it is necessary to enquire what Kind of Liquor this is, and how it moves, in order to determine how well its Nature and Motion are fitted for performing what is ex­pected from it.

49. It has been supposed, that the Liquor of the Nerves was of a very strong acid or alca­line Nature; but since we can see none of our Juices of such Natures, and since such Liquors irritate and destroy the Parts of the Body they are applied to, we can never imagine that the Brain could separate, or the Nerves could bear any Thing of such an acrid Nature; and this same Tenderness and Sensibility of these Or­gans must hinder us to suppose the Liquor of the Nerves can be acrid or pungent of any Kind, as of the Nature of inflammable Spirits, Spirit of Harthorn, &c.

50. Some have imagined the Liquor of the Nerves to be capable of vast Explosion, like Gunpowder, or of violent sudden Raretaction like Air, or of strong Ebullition like boiling Water, or the Mixture of Acids with alkaline Liquors. But as none of the Particles of our Mass of Blood, from which this Liquor of the Nerves must be derived, enjoy any such Pro­ [...]erties, we cannot suppose the Blood to fur­nish [Page 24]what it has not. Besides, all these Ope­rations are too violent for the Brain or Nerves to bear; and when once they are begun, are not so quickly controuled or put an End to, as Experience teaches us the Nerves can be made to cease from acting.

51. We know not sufficiently the Properties of an Aether pervading every Thing, to pretend to apply it to the animal Functions, especially where we must suppose it sent a great Way in a long Cord, in which we cannot conceive how it should be confined; which are Difficul­ties not to be surmounted in accounting for the Functions of Nerves by Means of such an Ae­ther.

52. The surest Way of judging what Kind of Liquor this of the Nerves must be, is to ex­mine the Liquors of similar Parts of the Body. All the Glands separate Liquors from the Blood much thinner than the compound Mass itself; such is the Liquor poured into the Cavity of the Abdomen, Thorax, Ventricles of the Brain, the Saliva, pancreatic Juice, Lymph, &c. Where­ever there is Occasion for secreted Liquors being thick and viscid, in order to answer bet­ter the Uses they are intended for, Nature has provided Reservoirs for them to stagnate in, where their thinner Parts may be carried off by the numerous absorbent Veins dispersed on the Sides of those Cavities, or by flying off where there is a Communication with the ex­ternal Air. The Snot of the Nose is very thick commonly by stagnating; but when the Se­cretion of the Membrane of the Nose is in creased by blowing the Nose, or by Sternuta­tories, we see it very thin and watry; there [Page 25]not then Time for the Air or Absorbents to carry off the more watry Particles. The Ce­rumen of the Ears is of a watry Consistence, when squeezed out before it has stagnated. The Mucus of the alimentary Canal is con­cocted in Lacunae. The Bile in the hepatick Duct is lymphatick; that in the Gall-bladder is viscid and strong. The Urine is much more watry as it comes from the Kidneys, than when it is excreted from the Bladder. The Seed is thin as it comes from the Testicles, and is concocted in the Vesiculae seminales, &c.

53. From § 52. we may safely conclude, that the Secretion of a thing Liquor is made in the Cortex of the Encephalon and Medulla spi­nalis; and seeing the Thinness of secreted Li­quors is generally as the Divisions of the Ves­sels into small subtile Branches, and the Ra­mifications within the Skull are carried on to a very great Subtilty, the Liquor secreted in the Encephalon may be determined to be among the finest or thinnest Fluids.

54. Seeing we can observe no large Reser­voire, where the Liquor secerned in the corti­cal Substance is deposited, to have its finer Parts taken off, we have Reason to think, that it goes forward into the Nerves in the same Con­dition in which it is secerned.

55. By fine or subtile animal Liquors is meant no more than those which are very flu­id, consisting of a large Proportion of watry Particles, and a lesser one of the oily, saline and terrestrious Particles. Some of the Li­quors which we can have in sufficient Quanti­ty to make Experiments with, are so fluid, and have so little Viscidity or Cohesion of Parts, [Page 26]that when laid on a Piece of clean Mirrour, they will evaporate without leaving a Stain on the Mirrour, such is the Liquor drilling out on the Surface of the Pleura, the Lymph, and se­veral others.

If then these Liquors, which are subject to our Examination, the secerning Vessels of which are so large that we can see them, have such a small Cohesion of Farts, it might not be unreasonable to say, that the Li­quor of the Nerves is as much more fine and fluid than Lymph, as the Vessels separating it are smaller; and therefore that the Fluid of the Nerves is a defecated Water with a very small Proportion of animal Sapo dissolved in it.

56. Two Experiments are said to contra­dict this Opinion of the Liquor of the Nerves being so fluid and subtile. One is, that upon cutting the Cauda equina of a living Anim [...]l, a Liquor as viscid as the White of an Egg drops out: The other is, that a wounded Nerve yields a glairy Sanies. But these are no Proof that the Liquor of the Nerves is of the same Nature, since it is evident that the Liquor dis­charged in both those Cases, comes out of the cellular Substance involving the nervous Fi­brils.

57. Considering how many Experiments make it evident, that there is a constant uninter­rupted Stream of Liquors flowing through all the Canals of Animals, which convey Li­quors, whose Particles are not larger than the Diameter of their Canal, which never is the Case in a natural State of excretory Vessels, it i [...] surprizing how the Opinion ever should have [Page 27]been taken up of the Liquid of the Nerves be­ing obliged to make such a prodigious rapid Course, as to flow from the Brain to each Muscle instantaneously when we will to con­tract it; or that this Liquor should flow back with the like Celerity from the Extremity of each Nerve, to which an Object of Sensation was applied. The Nerves, as well as the other Excretories of the Glands are always full of Liquors, the Degree of Distension of the Canals by the Liquors being, even in a sound natural State, sometimes more and some­times less, the Sides of the Tubes being stret­ched to make way for a larger Quantity, and contracting to accommodate themselves to a lesser Quantity; as much Liquor as does Vio­lence to the Sides of the Canals in stretching, or so little as the Sides cannot contract to, both occasion Diseases.

58. The Motion of the Fluid in the Nerves will not only then be constant, but it will also be equal, or nearly so: For tho' the Blood in the larger Arteries is moved unequally by the unequal Forces, the Contraction of the Ven­tricle of the Heart, and the weaker Power, the Systole of the Arteries, yet the Difference between these two moving Powers comes to be less and less perceptible, as the Arteries divide into smaller Branches, because of the nume­rous Resistances the Liquors meet with, and because the Canals they move in become larger, till in the very small arterious Branches there is no Difference in the Velocity of the Liquors from the Effect of the Heart or Arte­rie. The Motion of the Fluids must still be more equal in the Excretories of Glands, [Page 28]and particularly in those where the Vessels have divided into very minute Branches. So that the nervous Fluid will move constantly, equal­ly and slowly for ordinary; but this natural Course may be alter'd by the Influence of the Mind, or by the Pressure of some neighbour­ing active Organ.

59. We have perhaps no Idea of the Man­ner how Mind and Body act upon each other; but if we allow that the one is affected by the other, and that the Fluid of the Nerves (what­ever Name People please to give [...]t) is a prin­cipal Instrument which the Mind makes use of to influence the Actions of the Body, or to inform itself of the Impressions made on the Body, we must allow that the Mind can di­rect this Instrument differently, particularly as to Quantity and Celerity.

60. Let us now suppose the nervous Fluid such as has been argued for, to wit, an ex­treme Fluid saponaceous Water, moving in a constant, equal, slow Stream from the En­cephalon and Medulla spinalis in each of the proper nervous Fibres, except when the Mo­tion is changed by some accessory Cause, such as the Mind, Pressure of other Parts, &c. and let us examine how well such a Supposition will agree with the Phaenomena of the three great Functions, Nutrition, Sensation and muscular Motion, which the Nerves are prin­cipal Instruments of.

In general we may well enough say, that Nerves can carry Fluids to the most minute Part of the Body, to supply what is wasted in any of the solids; that the Impression made by the Objects of the Senses on the very soft pul­py [Page 29]Extremities of the Nerves of the Organs of the Senses, must make such a Stop in the e­qual-flowing nervous Fluid, as must instanta­neously be perceptible at the Fountain-head from which the pressed Pipes come; That the constant Flow of the Liquor of the Nerves in­to the Cavities of the muscular Fibrillae, occa­sions the natural Contraction of Muscles, by the constant nisus it makes to increase the transverse Diameter, and to shorten the longi­tudinal Diameter of each Fibre, and that it is only to allow the Mind a Power of pouring a greater Quantity of this same Fluid with a greater Velocity, into what muscular Fibres it pleases, to account for the voluntary strong A­ction of Muscles.

61. But since such a superficial Account would not be satisfactory, it will be expected, that the principal Phaenomena of these three Functions are to be explained by the Means of such a Fluid as has been supposed, and that the several Objections against this Doctrine should be answered: Let us attempt this, and where we cannot extricate ourselves from Difficul­ties which may be thrown in, let us boldly acknowledge Ignorance.

62. α. If Water, with a very small Propor­tion of Oils and Salts from the Earth, proves a fit Nourishment for Vegetables, such a Li­quor as the Fluid of the Nerves has been de­scribed (§ 55.) may not be unfit for repair­ing the Waste in Animals.

β. The slow constant Motion of this ner­vous Fluid (§ 57, 58.) to the most minute Parts of the Body (§ 9.) is well enough cal­culated to supply the Particles that are con­stantly [Page 30]carried away from the Solids by the Vis Vitae, Circulation of the Liquors and necessa­ry Actions of Life.

γ. The greater proportional Size of the En­cephalon, the great Fountain of this nutritious Liquor of the Nerves, in Creatures the youn­ger they are, seems very well calculated for their greater proportional Growth at that time of Life.

δ. A Palsy and Atrophy of the Members generally accompanying each other, shew, that Nourishment, Sensation and Motion do de­pend on the same Cause.

ε. It was said (§ 25.) that the Nerves were principal Instrum [...]nts in Nutrition, it was not affirmed, that they were the sole Instruments; and therefore an Atrophy may proceed from the Compression or other Lesion of an Artery, without being an Objection to the Doctrine here laid down.

63. a. All Objects of our Senses act by Im­pulse, when they are applied to their proper Organs. Tangible Objects evidently press on the Surface of our Bodies: Odorous Particles need the Assistance of Air moved rapidly to affect our Nose: Sapid Substances often are not sufficient to give us any Idea of their Taste by their own Weight, but need the Assistance of the Pressure of the Tongue upon the Palate: The Rays of Light collected into a Focus drive light Bodies before them: Sound communi­cates a Vibration to all Bodies in harmonic Proportion with it. The Impulse made thus by any of these Objects on the soft pulpy Nerves (§ 20.) which are full of Liquor, will press their Sides or Extremities, and their Li­quor [Page 31]will be hindred to flow so freely as it did. The Canals being all full, (§ 57.) this Resi­stance must instantaneously affect the whole Canals that are pressed and their Origins, and have the same Effect, as if the Impulse had been made upon the Origin itself. To illu­strate this by a gross Comparison, let any one push Water out of a Syringe through a long flexible Pipe, fixed to the Syringe, he will be sensible of Resistance, or a Push backwards instantaneously, as any other puts his Finger on the Orifice of the Pipe, or grips the Sides of it. This Impulse made on the Nerves, and thus communicated to their Origin, will vary ac­cording to the Strength or Weakness, the Quickness or Slowness, the Continuance or speedy Removal, the Uniformity or Irregula­rity, the Constancy or Alteration, &c. of the Application or the Objects to the Nerves.

b. Whenever the Impulse proper to the Ob­ject is regularly applied with due Force to a Nerve rightly disposed to be impressed by it, and is communicated, as just now explained, to the Sensorium, it gives a true and just Idea of the Object to the Mind.

c. The va [...]ious Kinds of Impulses, which the differ [...]n [...] Classes of Objects make, occa­sion a Nec [...]s [...]y of having the different Organs of the Senses variously modified, so that the several Impulses may be regularly applied to the Nerves in each Organ, or in other Words, we must have different Organs of the Senses fitted to the different Classes of Objects.

d. As the Objects have one common Pro­perty of Impulse, so all the Organs have most of the Properties of the Organ of Touching in [Page 32]common with the Papillae the Skin. In the Nose and Tongue this is evident; in some O­perations on the Eyes we can also perceive this, as we may likewise do in some Cases, where Matter is collected in the internal Ear.

e. These Properties common as well in the Objects as the Organs, occasion frequently uncommon Effects in the Application of an Object to an Organ proper to another Object of Sensation; for sometimes we have the same Idea, as if the Object had been applied to its own proper Organ; at other times the Object is as it were changed, and we have the Idea as if the Organ had had its own proper Object applied to it. Thus, for Example, Light is the proper Object to be applied to the Eye, to give us any Idea of Colours; yet when all Light is excluded from the Eyes, an Idea of Light and Colours may be excited in us by Coughing, Sneezing, Rubbing, or striking the Eye-ball.— A Cane vibrating by a Stroke, but not so as to give any Sound perceptible to the Ear, if it is applied to the Teeth, it raises a strong Idea of Sound, as will also a little In­sect crawling in the Meatus auditorius.—The Fingers applied to two rough Surfaces, rub­bing on each other, are sensible of the Sound they make; Surgeons of any Practice in the Cure of fractured Bones can bear Witness to the Truth of this.— The Fingers dipped in acid and several other acrid Liquors, have a Sensation very like to Tasting.— Sm [...]lling and Tasting every Body knows are subservien [...] and assisting to each other. From such Ex­amples we have further Proof of one genera [...] Cause of our Sensations, to wit, Impulse [Page 33]from the Objects; and that any one of the Or­gans would be capable of producing the Effect of another, if the Impulses of the different Objects could be [...]regularly appl [...]ed to each.

f. If the Impulse of an Object is applied with due Force, but irregularly, a confused Idea of the Object is raised. Distant Objects are confus'd to Myopes, as very near ones are to Presbytae.

g. If the Application of the Impulse is re­gular, but the Force with which it is applied is too weak, our Perception of the Object is too faint. One may whisper so low as not to be heard.

h. If the Application of Objects is too vio­lent, and there is any Danger of the tender Organs of our Senses being lesed or destroyed, the uneasy Sensation we call Pain is raised, whatever the Organ thus lesed is. The Objects of Touch affect every Organ: Thus Pr [...]ssure, cutting, pricking, Salts, pungent Oils, great Heat, violent Cold, &c. occasion Pain, whereever they are applied. Besides this, e­very particular Organ can be affected with Pain, by the too violent Application of its own proper Object. Too much Light pains the Eyes; very loud Sound stuns the Ears; very o­dorous Bodies and too sapid Objects hurt the Nose and Tongue. A pretty sure Proof this of the Objects of our Senses all acting, and of the Organs all being impressed in nearly the same Way.

i. Whenever this uneasy Sensation, Pain, is thus raised, a Sort of Necessity is as it were imposed upon the Mind, to endeavour to get free of the injuring Cause, by either withdraw­ing [Page 34]the lesed Part of the Body from it, as one retires his Hand when his Finger is pricked or burnt; or the injuring Cause is endeavoured to be forced from the Body, as a Tenesmus pushes acrid Faeces out of the rectum. In both these Operations a convulsive Contractio [...] is immediately made in the lesed Part, or in the Neighbourhood of it; and if the Irritation is very strong or permanent, the greater Part of the nervous System comes to be affected in that spasmodic or convulsive Way.

This Nisus of the Mind to free the Body of what is in Danger of being very hurtful, may serve to explain the Phaenomena of a great many Diseases, when we are acquainted with the Distribution of the part [...]cular Nerves; and from this we can understand the Operation of Medicines that stimulate, and may learn how by exciting a sharp but momentary Pain, we may free the Body of another Pain that would be more durable; and that by having it thus in our Power to determine a flow of the Liquor of the Nerves to any particular Part, for the Benefit of that Part or the Relief of any other diseased Part, we can do considerable Ser­vice by a right Application of the proper Me­dicines.

k. If a Pain-giving Cause is very violent or long continued, it destroys the Organs either irrecoverably, or puts them so much out of Order, that they only gradually recover. People have been made blind or deaf for al [...] their Lives after, by the violent Effect of Ligh [...] on their Eyes or Sound on their Ears, and w [...] are frequently exposed to as much Light an [...] Sound as make us unfit to see or hear for a [Page 35]considerable Time after. I would explain this by a Ligature put round the tender Branch of an Herb; this Ligature drawn to a certain De­gr [...]e may weaken the Canals so as to be unfit for the Circulation of the Juices a good While, till they are gradually explicated and made firm by these Juices. A stricter Ligature would disorder the Structure of the Fibres so much, that the Liquors could not recover them. The Analogy is so plain it needs no Commentary.

64. 1. In applying the Fluid of the Nerves to the Action of Muscles, it was said that natu­ral or involuntary Contraction of Muscles was the Nisus which the nervous Fluid flow­ing constantly into the muscular Fibres makes to distend these Fibrils, by enlarging their transverse Diameters and shortning their Axes, and that voluntary Contraction was owing to a greater Quantity of that nervous Liquor de­termined towards the Muscle to be put in Action, and poured with a greater momentum into the muscular Fibrils by the Power of the Mind willing to make such a Muscle to act.

2. It has been objected to this account of muscular Motion, that if it was true, the Volume of a Muscle in Contraction neces­sarily would be considerably increased by so much Liquor poured into its Fibrils, whereas it does not appear by any Experiment, that the Volume of a Muscle is increased by its being put into Action.

3. To th [...]s it has been answered, That the [...]paces between the muscular Fibres are suf­ici [...]nt to [...]llow th [...] Fibrils swelling during the Contraction of a Muscle to lodge in, without [Page 36]any Addition to the Bulk of the Muscle; and that it plainly appears that these Spaces be­tween the Fibrils are thus occupied, by the Compression which the larger Vessels of M [...]s­cles, which run in those Spaces, suffer during the Action of a Muscle; it is so great that the Muscle becomes p [...]le by contract [...]ng.

4. Another Objection to the Action of Muscl [...]s being owing to the Influx of a Fluid into their Fibrils is, that muscular Fibres are distractile, or capable or being stretched; and therefore when a Fluid is poured into their hollow Fibrils, they would be stretched longi­tudinally, as well as have their transverse Dia­meters increas [...]d, that is, a Muscle would be­come longer as well as thicker when it is put in Action, whereas it is known to every Body that a Muscle is shortned when acting.

5. In Answer to this it has been remarked, that tho' muscular Fibrils are distractile, yet, they will not yield to, or be stretched by every Force however little that m [...]ght be applied to them, a Cord that can be stretched in Length by the Weight of a Pound or two, might not yield in the least to an Ounce or two; and it must likewise be observed, that gradually as any Body is stretched, its Resistance to the stretching force increases. A Rope may be stretched to a certain Length by a Pound Weight appended to it, which would require two Pounds to stretch it very little further; and therefore the general Observation of Ani­mal Fibres being distractile, cannot be a rea­sonable Objection to the account of muscular Motion above-ment [...]oned, unless a Proof is brought that the Force which the Liquid of [Page 37]the Nerves must exert upon each Fibre of a Muscle in order to make a Muscle act, is ca­pable of distracting or stretching the Fibres, which has not yet been attempted to be proved.

6. If muscular Motion depends on the In­flux of the nervous Liquid, the instantaneous Contraction of a Muscle, when the Mind wills to make it act, will easily be understood from the Nerves being always full of their Liquor, (§ 57.)

7. If either the Nerves of any Muscle do not furnish a sufficient Quantity of their Li­quor, or if the Fibres of a Muscle become too easily distractile, such a Muscle will be un­active or paralytick.

8. If too great a Quantity of the Liquor of the Nerves is determined to a Muscle or Muscles, by any Cause which the Mind can­not command, such Muscle or Muscles will be convulsed.

9. If the Motion of the Liquid of the Nerves is not uniform, but by Disease becomes irre­gular, an alternate Relaxation and Contracti­on of Muscles may be the Consequence, hence trembling Palsies, chorea sancti Viti, &c.

10. Tho' the Nerves may not furnish as much Liquor as may be sufficient to make Muscles contract with Strength enough to overcome the Resistances to their Action, yet there may be enough of Liquor in the Nerves to allow the Impressions of Objects to be con­veyed to the sensorium; this may be one Cause of a Member's being sometimes sensible after it cannot be moved.

11. Unless the Liquor of the Nerves ac­quires some Energy in the Brain, which we [Page 38]have no Reason to think the Circulation of the Fluids in the Vessels can give it, or unless it has Properties other than what we can disco­ver in it, or unless there is an active Agent de­termining its momentum towards some parti­cular Parts, which we are not conscious of; if some of these don't obtain the Action of the Heart continuing of equal Force to propel our Liquors, notwithstanding all the Resist­ances that are to it, is not to be explained.

12. All Muscles, but especially the Heart, will continue to contract in an irregular Way, after they are cut away from the Animal to whom they belonged, which may be owing to the Liquors continuing to flow in the small Vessels, and being poured irregularly into the muscular Fibrillae.

13. After the Heart or any other Muscle cut away from an Animal has ceased to con­tract, its Contraction may again be restored by blowing one's warm Breath upon it, or pricking it with any sharp Instrument; that Heat or Prick [...]ng should by their stimulus (§63. 1.) occasion Contraction in a living Creature may be understood; but how they should have the same Effect in a Muscle se­parated from an Animal, I know not.

N. B. Num. 11, 12, 13 are as inexpl [...] ­cable upon any other Supposition yet made concerning muscular Motion.

65. I know no Experiment or Observati­ons by which any Thing can be proved, or from which any Thing can be reasonably in­ferr [...] con [...]erning the Uses of the Ganglions of th Nerves, and therefore pretend to g [...]ve no Account of them.

Of the particular Nerves.

THERE are generally said to be forty Pair of Nerves in all, of which ten come out from the Encephalon, and the other thirty have their Origin from the Medulla spinalis.

Of the ten Pair of Nerves that are generally said to come from the Encephalon, the first is the OLFACTORY, which long had the Name of the Mammillary Processes of the Brain, be­cause in the Brutes which were most com­monly dissected, their Form has some Resem­blance to a Nipple; for they are large where they begin to go out from the Brain, and taper a little as they go forwards to the cribriform Part of the Ethmoid Bone; and because in these Animals they are evidently Continuations or Productions of the two anterior Ventricles of the Brain, being hollow and contain­ing Lymph, the Antients believed that these Nerves served to convey the superfluous Mucus from the cold moist Brain, to be evacuated by the Holes of the cribriform Bone into the Nose. But in Man these Nerves are small, long, and without any Cavity, having their Origin from the corpora striata, near the Part where the internal carotid Arteries are about to send off their Branches to the different Parts of the Brain, and in their Course under the an­ [...]erior Lobes of the Brain, which have a De­pression made for lodging them, the human olfactory Nerves become larger till they [...]ome to the cribriform Bone where they split [...]nto a great Number of small Filaments to pass thro' the little Holes in that Bone, and [Page 40]then each being joined by a Franch of the fifth Pair of Nerves is spread on the Membrane of the Nose.

The tender Structure and sudden Expansion of these Nerves on such a large Surface ren­der it impossible to trace them far; which has made some Authors deny them to be Nerves: But when we break the Circumference of the cribriform Lamella, and then gently raise it, we may see the Distribution of the Nerves some way on the Membrane of the Nose.

The Contrivance of defending these long soft Nerves from being too much pressed by the anterior Lobes of the Brain under which they lye, is singular, because they have not only the prominent orbitar Processes of the frontal Bone, and the Crista Galli of the Eth­moid Bone to support the Brain on each Side, with the Falx by means of the Veins going in­to the longitudinal Sinus, and other Attach­ments bearing it up in the Middle, but have a Groove formed in each Lobe of the Brain itself for them to lodge in. Their splitting into so many small Branches before they enter the Bones of the Skull is likewise peculiar to them; for generally the Nerves come from the Brain in disgregated Filaments, and unite into Cords, as they are going out at the Holes of the Bones: But we shall find that this Con­trivance is the best for answering the Purpose they are designed for, of being the Organ of smelling; for had they been expanded upon the Membrane of the Nose into a medullary Web, such as the optic Nerve forms, it would have been too sensible to bear the Im­pressions of such Objects as are applied to it, [Page 41]and a Distribution in the more common way of a Cord sending off Branches, would not have been equal enough for such an Organ of Sensation.

The 2 d Pair of Nerves are the OPTIC, which rise each from the thalami nervorum op­ticorum, and then after making a large Curve outwards, run obliquely inwards and for­wards till they unite at the Fore-part of the Sella Turcica, and then dividing again, each runs obliquely forwards and outwards to go out at its proper Hole in the sphenoid Bone, accompanied with the proper ocular Artery, to run afterwards to the Globe of the Eye, within which each is extended into a very fine Cup-like Web that lines all the In-side of the Eye as far forwards as the ciliary Circle, and is universally known by the Name of Retina.

Tho' the Substance of these two Nerves seems to be blended at the Place where they are joined, yet Observations of People whose optic Nerves were not joined at all, and of others who have been blind of one Eye from a Fault in the optic Nerve, or in those who have had one of their Eyes taken out, make it appear that there is no such intimate Union of Substance, the optic Nerve of the affected Side only being w [...]sted, while the other was large and plump; and the same Observations are contradictory to the Doctrine of a Decus­sation of all the Nerves (§ 7.); for the Disease could be traced from the affected Eye to the Origin of the Nerve on the same Side. In many Fishes indeed the Doctrine of Decussa­tion is favoured, for their optic Nerves plain­ly [Page 42]cross each other without any Union at the Part where they are joined in Men and most Quadrupeds.

Those People, whose optic Nerves were not joined, having neither seen Objects double, nor turned their Eyes different Ways, is also a plain Proof that the Conjunction of the op­tic Nerves will not serve to account for either the uniform Motions of our Eyes, or our seeing Objects single with two Eyes.

The Retina of a recent Eye, without any Preparation, appears a very fine Web, with some Blood-vessels coming from its Center to be distributed on it; but after a good In­jection of the Arteries that run in the Sub­stance of this Nerve as is common to o­ther Nerves, it is with Difficulty that we can observe its nervous medullary Substance. As these Vessels are placed in the centrical Part of the optic Nerve, and there are not medul­lary Fibres here, where it enters the Ball of the Eye: This may be one Reason why we do not see such Bodies or Parts of Bodies, whose Picture, formed on the Bottom of our Eye, falls on this centrical Part of the Retina. An In­flammation in those Arteries of the Retina, which an Opthalmia is generally attended with, may very well account for that Tenderness in the Eyes, and Inability to bear the Light which People have in that Disease. The Over-dis­tension of these Vessels may likewise serve to account for the black Spots observed on bright coloured Bodies especially, and that smoaky Fog, thro' which all Objects are seen by People in some Fevers. If those Vessels lose their Tone and remain preternaturaly distended, no [Page 43]Objects may affect our Retina, tho' the Eye externally appears sound, or this may be one Cause of an Amaurosis or Gutta serena.

The THIRD PAIR rise from the anterior Part of the Processus annularis, and piercing the Dura Mater a little before and to a Side of the lateral Extrem [...]ties of the posterior clinoid Process of the sphenoid Bone, run along the Receptacula, or cavernous Sinuses, at the Side of the Ephippium, to get out at the Foramina lace­ra, to be distributed to the Globe of the Eye, to the Musculus rectus of the Palpebra, and to the Attollens, Adductor, Deprimens and obli­quus minor Muscles of the Eye-ball. These Muscles being principal Instruments in the Motions of the Eye-lid and Eye-ball, the Nerve has therefore got the Name of the Mo­tor Oculi. I have frequently observed in Con­vulsions the Eye-lids widely opened, the Cor­nea turned up and outwards, and t [...]e Eye-balls sunk in the Orbit; which well described the conjunct Action of the Muscles which this Pair of Nerves serves. Possibly the Distension of a consi [...]erable Branch of the Carotid, which passes over this Nerve near its Origin on each Side, may be the Reason of that Heaviness in the Eye-lids and Eyes, after drinking hard or eating much.

The FOURTH PAIR, which are the smal­lest Nerves of any, derive their Origin from the posterior Base of the Testes, and then mak­ing a long Course on the Side of the annular Protuberance, enter the Dura Mater a little farther back and outwards than the third Pair, to run also along the Receptacula, to pass out at the Foramina lacera, and to be entirely spent [Page 44]on the Musculi trochleares, or superior oblique Muscles of the Eyes. The rotatory Motions and the Advancement of the Eye-balls forward, by which Motions several of our Passions are expressed, principally depending on these Mus­cles, the Nerves that serve them have got the Name of PATHETICI.

The FIFTH PAIR are large Nerves, ri­sing from the annular Process, where the me­dullary Processes of the Cerebellum join in the Formation of that Tuber, to enter the Dura Mater near the Point of the petrous Process of the Temporal Bones, and then plunging into the Receptacula at the Side of the Sella Turcica, each becomes in appearance thicker, and goes out of the Skull in three great Branches.

The first Branch of the 5th is the O­PHTHALMICK, which runs through the Foramen lacerum to the Orbit, having in its Pas­sage thither a Connection with the 6th Pair: it is afterwards distributed to the Ball of the Eye with the 3d, to the Nose, along with the Ol­factory, which the Branch of the 5th that passes through the Orbiter internus Hole, joins in the Manner already mentioned in the Description of the first Pair. This ophthalmic Branch like­wise supplies the Glandula lacrymalis, Fat, Membranes, Muscles and the Teguments of the Eye-lids, its longest farthest extended Branch passing through the Foramen superciliare of the Os Frontis to be distributed to the Forehead.

The small Fibres which this first Branch of the 5th and the third Pair of Nerves send to the Eye-ball, being situated on the [...]optic Nerve, and after piercing the sclerotick Coat running on the choroid Coat on the Outside of the Re­tina [Page 45]in their Course to the Uvea or Iris, may possibly be a Reason, why there is such a Sym­pathy between the optic Nerve and the Uvea, that the Uvea contracts to lessen the Pupil, and exclude too numerous Rays of Light; and this, with the Sympathy which must arise from some of the Nerves of the Membrane of the Nostrils being derived from this first Branch of the 5th Pair of Nerves, may also be the Cause, why a strong Irritation of too strong Light up­on the Retina may produce the same Effect, Sneezing, as when any tickling Substance is applied to the Membrane of the Nose. In the Megrim all the Branches of this Nerve disco­ver themselves to be affected; for t [...]e Forehead is racked with Pain, the Eye-ball is pain'd, and feels as if it was squeezed, the Eye-lids shut convulsively, the Tears trickle down, and an uneasy Heat is felt in the Nose Hence we can understand, where external Medicines will have the best Effect, when applied to re­move this Disease, to wit, to the Membrane of the Nose and to the Forehead. Hence we can understand, why alternate Pressure near the superciliary Hole of the frontal Bone some­times gives immediate Relief in the Megrim.

The second Branch of the 5th Pair of Nerves may be called MAXILLARIS SU­PERIOR, from its serving principally the Parts of the upper Jaw. It goes out at the round Hole of the sphenoid Bone, and sends immediately one Branch in the Channel on the Pop of the Antrum maxillare, the Membrane of which and the superior Teeth are supplied by it in its Passage. As it is about to go out [...]t the Orbiter externus Hole, it sends a Nerve [Page 46]through the Substance of the Os maxillare, to come out at Steno's Duct, to be distributed to the anterior Part of the Palate; and what re­mains of it escaping at the Orbiter externus Hole, divides into a great many Branches, that supply the Cheek, upper Lip and Nostril. The next considerable Branch of the superior maxillary Nerve is sent into the Nose by the Hole common to the Palate and sphenoidal Bone, and the remaining Part of this Nerve runs in the Palato-maxillaris Canal, giving off Branches to the Temples and Pterygoid Mus­cles, and comes at last into the Palate to be lost. Hence the Ach in the Teeth of the up­per Jaw occasions a gnawing Pain deep seated in the Bones of the Face, with a Swelling in the Eye-lids, Cheek, Nose and upper Lip; and on the other hand, an Inflammation in these Parts is often attended with sharp Pain in the Teeth. Hence an Obstruction in the Duct of the maxillary Sinus, which obliges the Liquor secreted there to find out a preter­natural Rout for itself, as I have seen more than once, may be occasioned by the Pain of the Teeth.

The third or MAXILLARIS INFERIOR. Branch of the fifth Pair going out at the oval Hole of the sphenoid Bone, serves the Muscles of the lower Jaw, and the Muscles situated between the Os hyoides and Jaw; all the sali­vary Glands, the Amygdalae and the external Ear have Branches from it; it has a large Branch lost in the Tongue, and sends another through the Canal in the Substance of the low­er Jaw, to serve all the Teeth there, and to come out at the Hole in the anterior Part of [Page 47]the Jaw, to be lost in the Chin and Under-lip-Hence a convulsive Contraction of the Mus­cles of the lower Jaw, or the Mouth's being involuntarly shut, a great Flow of Spittle or Salivation, a Pain in the Ear especially in De­glutition, and a Swelling all about the Throat, are natural Consequences of a violent Irritation of the Nerves of the lower Teeth in the Tooth-ach; and Pain in the Teeth and Ear is as natural a Consequence of an Angina. Hence alternate Pressure on the Chin may sometimes relieve the Violence of a Tooth-ach. Hence destroying the Nerves of a Tooth by actual or potential Cauteries, or pulling a carious Tooth, so often removes immedi [...]tely all these Symptoms. Hence no Cure is to be found for some Ulcers in the upper or lower Jaw, but by drawing a Tooth.

The SIXTH PAIR, which is the smallest except the fourth, rises from the Forepart of the Corpora pyramidalia, and entring the Dura Mater some way behind the Extremities of the posterior clinoid Processes of the sphenoid Bone, have a long Course below that Membrane, and within the Receptacula at the Side of the Sella Turcica, to go out at the Foramina lacera into the Orbit, tolbe lost in the Abductor-muscle of the Eye. In this Passage each of them lies very contiguous to the internal carotid Artery, and to the ophthalmick Branch of the fifth Pair of Nerves. At the same Place where they are contiguous to the Carotid, a Nerve, e [...]er, ac­ [...]ording to the general Description of Anato­ [...]ists, goe from each of them [...]n an uncom­ [...]on w [...]y (th [...]t is the Angle is obt [...]se beyond [...]ere [...] rises) to descend with the Artery, and [Page 48]to form the Beginning of the intercostal Nerve; or, according to other Authors, this Nerve comes up from the great Ganglion of the Inter­costal to be joined to the sixth here.

The Arguments for this latter Opinion are, That according to the common Opinion, this Beginning of the intercostal Nerve, as 'tis cal­led, would rise in a Manner not so ordinary in Nerves. In the next Place it is observed, that the sixth Pair is larger nearer to the Orbit, than it is before it comes to the Place where this Nerve is said to go off; and therefore it is more probable, that it receives an Addition there rather than gives off a Branch. Lastly, It is found, that upon cutting the intercostal Nerves of living Animals, the Eyes plainly were affected, they lost their bright Water, the Gum, or Gore, as we call it, was separated in greater Quantity, the Pupil was more contra­cted, the cartilaginous Membrane at the inter­nal Canthus came more over the Eye, and the Eye-ball itself was diminished.

To this it is answered in Defence of the more common Doctrine, that other Branches of Nerves go off in a reflected Way as well as this does, supposing it to be the Beginning of the Intercostal, and that the Reflection would rather be greater, if it is thought to come up from the Intercostal to the sixth. 2 dly, Tha [...] Nerves enlarge sometimes where there is no Addition made to them, as in the Instance already mentioned of the Trunk of the fifth Pa [...] while below the Dura Mater. 3 dly, That th [...] Experiments on living Animals shew indeed that the Eyes are affected upon cutting the in­tercostal Nerve, but not in the Way mig [...] [Page 49]have been expected, if the Intercostal furnishes such a Shareof the Nerve that goes to the Abdu­ctor Muscle of the Eye; for it might have been thought, that this Muscle would have been so much weakned immediately upon cutting the Intercostal, as its Antagonist the Adductor would have greatly prevailed over it, and have turned the Eye strongly in towards the Nose, which is not said to be a Consequence of this Experiment. So that the Arguments are still e­quivocal, and more Observations and Experi­ments must be made before it can be determined with Certainty, whether the sixth Pair gives or receives a Branch here. In the mean time I shall continue to speak about the Origin of the Intercostal with the common Herd of Anato­mists.

At this same Place where the Intercostal be­gins, the fifth Pair is contiguous and adherent to the sixth; and it is generally said, that the ophthalmic Branch of the fifth gives a Branch or two to the Beginning of the Intercostal, or receives such from it. Others deny any such Communication between them, and those who affirm the Communication confess, that in some Subjects they could not see it. After examining the Nerves here in a great many Subjects, I cannot determine whether or not there are nervous Filaments going from the one to the other. Sometimes I thought I traced them evidently; at other times I ob­served what I dissected for nervous Filaments, to be no other than collapsed cellular Sub­stance; and in all the Subjects where I had pushed an Injection successfully into the very small Arteries, I could only observe a Plexus [Page 50]of Vessels connecting the one to the other. In any of these Ways however there is as much Connection, as we are assured from many Ex­periments and Observations on other Nerves, is sufficient to make a very great Sympathy among the Nerves here. Possibly the Appear­ances in the Eyes of Dogs, whose intercostal Nerves were cut, might be owing to this Sym­pathy.

The SEVENTH PAIR comes out from the lateral Part of the annular Process, behind where the medullary Processes of the Cerebel­lum are joined to that Tuber, and, being ac­companied w [...]th a larger Artery than most o­ther Nerves, enters the internal Meatus audi­torius, where soon the two great Pacquets of Fibr [...]s, of which it appeared to consist within the Skull, separate from each other; one of them enters by several small Holes into the Vestible, Cochlea and semicircular Canals, is stretched on this inner Camera of the Ear in a very soft pulpy Substance; and being never seen in the Form of a firm Cord, such as the other Packet of this Nerve and most other Nerves become, is called PORTIO MOL­LIS of the auditory Nerve.

The other Part of this seventh Pair passes through Galen's Foramen caecum or Fallopius's Aqueduct in its crooked Passage by the Side of the Tympanum, in which Passage a Nerve sent from the lingual Branch of the inferior maxil­lary Nerve, along the outside of the Tuba Eu­stachiana, and cross the Cavity of the Tympa­num, where it has the Name of Chorda Tym­pa [...], [...]s commonly said to be joined to it. The very acute Angle which this Nerve makes with [Page 51]the fifth, or the sudden violent Reflexion it would suffer, on the Supposition of its coming from the fifth to the seventh, whereas suppo­sing its Course from the seventh to the fifth, its Course would be more in the ordinary Way, has made some say, that this Chorda tympani should be esteemed a Branch of the seventh Pair going to join the fifth. This same smaller Packet of the seventh gives Branches to the Muscles of the Malleus and to the Dura Mater, while it passes through the bony crook­ed Canal, and at last comes out in a firm Cord named PORTIO DURA, at the Extremity of this Canal, between the styloid and mastoid Processes of the temporal Bone, giving imme­diately Filaments to the little oblique Muscles of the Head, and to those that rise from the styloid Process. It then pierces through the parotid Gland, and divides into a great many Branches, which are dispersed in the Muscles and Teguments that cover all the Side of the superior Part of the Neck, the whole Face and Cranium, as far back as the Temples, in­cluding a considerable Part of the external Ear. Its Branches having thus a considerable Con­nection with all the three Branches of the fifth Pair, and with the second cervical, occasions a considerable Sympathy of these Nerves with it. Hence in the Tooth-ach, the Pain is some­times very little in the affected Tooth, com­pared to what it is all along the Side of the Head and in the Ear. Hence probably the Re­lief of the Tooth-ach by Blisters applied behind the Ear, or by a hot Iron touching the Antihe­lix of the Ear. By this Communication or Con­nexion possibly too it is, that a vibrating String [Page 52]held between one's Teeth, gives him a strong Idea of its Sound which no other can hear. Perhaps too the Distribution of this Nerve oc­casions the Head to be so quickly turned upon the Impression of Sound on our Ears.

The EIGHTH PAIR of Nerves rise from the lateral Base of the Corpora olivaria in dis­gregated Fibres, and as they are entring the anterior internal Part of the Hole, common to the Os Occipitis and Temporum, each is joined by a Nerve which ascends within the Dura Mater from the 10th of the Head, the first and second cervical, and sometimes from inferior Nerves: This every Body knows has the Name of the NERVUS ACCESSORIUS. When the two get out of the Skull, the Accessorius separates from the eighth, and descending ob­liquely outwards, passes through the Sterno­mastoideus Muscle, to which it gives Branches to be lost in the Trapezius and Rhomboid Mus­cles of the Scapula. In this Course it is ge­nerally more or less joined by the second cer­vical Nerve.

The large eighth Pair soon after its Exit gives Nerves to the Tongue, Larynx, Pha­rynx and Ganglion of the Intercostal Nerve, and being disjoined from the 9th and Interco­stal, to which it adheres closely some way, runs straight down the Neck behind the inter­nal jugular Vein, and at the interior Side of the internal carotid Artery. As it is about to enter the Thorax, a large Nerve goes off from the eighth of each Side: This branch of the right Side turns round from the anterior to the posterior Part of the subclavian Artery, while the Branch of the left Side turns round the great [Page 53]Curve of the Aorta, both of them mounting up again at the Side of the O Esophagus, to which they give Branches, are lost at last in the La­rynx. These are called the RECURRENT Nerves, which we are desired to shun in the Operation of Bronchotomy, tho' their deep Si­tuation protects them sufficiently. The Mu­scles of the Larynx being in a good measure supplied with Nerves from the Recurrents, it is to be expected, that the cutting of them will greatly weaken the Voice, tho' it will not be entirely lost, so long as the superior Branches of the eighth Pair are entire.

At or near the Place where the recurrent Nerves go off from the eighth Pair, or frequent­ly from the Recurrents themselves, Nerves go off to the Pericardium, and to join with the Branches of the Intercostal that are distributed to the Heart.

After these Branches are sent off, the Par­vagum on each Side descends behind the great Branch of the Trachea and gives numerous Fi­laments to the Lungs in going to the O E [...]opha­gus. The one of the left Side running on the Forepart of the O Esophagus, communicates by several Branches with the right one in its Descent to be distributed to the Stomach: The right one gets behind the O Esophagus, where it splits and rejoins several Times be­fore it arrives at the Stomach, to which [...]t sends Nerves; and then being joined by a Branch from the left Trunk, they run towards the caeliac Artery, there to join into the great semi­lunar Ganglion formed by the two Intercostals.

From the Distribution of this Par vagum, we may learn how tickling the Fauces with a [Page 54]Feather or any such Substance, excites a Nau­sea and Inclination to vomit. Why cough­ing occasions vomiting, or vomiting raises a Cough. Hence we see how the nervous Asthma and the Tussis convulsiva, Kinkcough, are attended with a straitning of the Glottis. How Food ill to digest brings on the Asthma on weakly People, and why Emetics have fre­quently cured the Asthma very speedily. How the superior Orifice of the Stomach is so sensi­ble as to be looked on as the Seat of the Soul by some. How People subject to Distensions of the Stomach have so often the Sensations of Balls in their Breast or Throats. Why the Globus hystericus is so often attended with a violent Strangulation at the Glottis. The Sym­pathy among the Branches of these Nerves will lead us to understand these and several o­ther Phaenomena.

The NINTH PAIR of Nerves comes from the inferior Part of the Corpora pyramidalia, to go out of the Skull at their proper Holes of the occipital Bones. After their Egress they adhere for some way firmly to the 8th and Intercostal, and then sending a Branch that in many Subjects is joined with Branches of the first and second cervical Nerves, to be distri­buted to the Thyroid Gland and Muscles on the Fore-part of the Trachea Arteria, the 9th is lost in the Muscles and Substance of the Tongue. Some have thought this Nerve, and others have esteemed the third Branch of the fifth Pair of Nerves to be the proper gustatory Nerve. I know no Observations or Experi­ments to prove either Opinion, or to deter­mine that both the Nerves may not serve for [Page 55]Tasting, and for the Motion of the Tongue.

The TENTH PAIR rises from the Sides of the Medulla spinalis, to go out between the Os Occipitis and first Vertebra of the Neck. After each of them gives a Branch to the great Ganglion of the Intercostal Nerve, they are distributed to the oblique Muscles, and to some of the Extensors of the Head. Whether the Name of the tenth of the Head, or of the first Vertebral, ought to be given to this Nerve, is of no such Consequence as to deserve a Debate.

In the Description of the sixth Pair, I said that I would use the way of speaking which most Anatomists have, to wit, I would say that the Beginning of the Intercostal Nerve comes out of the Skull, and therefore sh [...]ll here subjoin a cursory Description of this Nerve to those of the Head, notwithstand [...]ng its much larger Part is composed of Nerves coming out from the Medulla spinalis. There is no greater Incongruity in Point of Method to say, that a Nerve one is describing receives Additions from Nerves that have not been de­scribed, than it is to repeat in the Description of a great many Nerves, that each of them gives Branches to form a Nerve which we are ignorant of, which is all the Difference be­tween describing the Intercostal before or after the spinal Nerves.

The Branch reflected from the sixth Pair, joined possibly by some Filaments of the O­phthalmic Branch of the fifth, runs along with the internal Carotid thro' the crooked Canal formed for this Artery in the temporal Bone, where the little Nerve is very soft and pappy, [Page 56]and in several Subjects divides and unites a­gain before it comes out of the Skull. As soon as the Nerve escapes out of this bony Ca­nal it is connected a little way with the eighth and ninth, then separating from them, after seeming to receive additional Nerves from them, it forms a large Ganglion, into which Branches from the tenth of the Head, and from the first and second cervical enter. From this Ganglion the Nerves come out again small to run down the Neck along with the carotid Artery, communicating by Branches with the cervical Nerves, and giv­ing Nerves to the Muscles that bend the Head and Neck. As the Intercostal is about to en­ter the Thorax, it forms another Ganglion from which Nerves are sent to the Trachea and to the Heart; these designed for the Heart joining with the Branches of the eighth, and passing between the two great Arteries and the Auricles to the Substance of that Muscle. The Intercostal after this being composed of two Branches, one going behind, and the o­ther running over the anterior Part of the Sub­clavian Artery, forms a new Ganglion where the two Branches unite below that Artery, and then descending along the Sides of the Verte­brae of the Thorax, receives Branches from each of the dorsal Nerves, which Branches appearing to come out between the Ribs, have given the Name of Intercostal to the whole Nerve. Where the Addition is made to it from the fifth dorsal Nerve, a Branch goes off ob­liquely forwards, which being joined by other such Branches from the sixth, seventh, eighth and ninth darsal, an anterior Trunk is form­ed [Page 57]that passes between the Fibres of the Ap­pendix musculosa of th [...] Diaphragm to form a­long with the other Intercostal and the Branches of the eighth Pair, a large semilunar Ganglion situated betw [...]n the caeliac and superior me­senteric Arteries; the Roots of which are, as it were, involved in a sort of nervous Net­work of this Ganglion, from which a great Number of very small nervous Threads run out to be extended on the Surface of all the Branches of these two Arteries, so as to be easily seen when any of the Arteries are stretch­ed, but not to be dissected off from them; and thus the Liver, Gall-Bladder, Duodenum, Pan­creas, Spleen, Jejunum, Ilium, and a large Share of the Colon have their Nerves sent from this great solar Ganglion or Plexus.

Several Fibres of this Ganglion running down upon the Aorta, meet with other Nerves sent from the posterior Trunk of the Inter­costal, which continues its Course along the Sides of the Vertebrae, they supply the Glandulae renales, Kidneys and Testes in Men or Ovaria in Women; and then they form a Net-work upon the inferior mesenteric Artery where the Nerves of the two Sides meet, and accom­pany the Branches of this Artery to the Part of the Colon that lies in the left Side or the Belly, and to the Rectum as far down as the lower Part of the Pelvis.

The Intercostal continuing down by the Side of the Vertebrae of the Loins, is joined by Nerves coming from between these Ver­ [...]ebrae, and sends Nerves to the Organs of Generation and others in the Pelvis, being [Page 58]even joined with those that are sent to the in­ferior Extremities.

The almost universal Connection and Com­munication this Nerve has with the other Nerves of the Body, may lead us to under­stand a great many Phaenomena, where one otherwise would be greatly surprized at the Sympathy to be observed among the Parts of the Body. One who knows the Course of this Nerve will readily understand why a Stone in the Kidneys, or Ureters, or any other Cause irritating those Organs, should so much more frequently bring on Vomiting and other Dis­orders of the Stomach, than the Stone or any other stimulating Cause in the Bladder does. The Obstructions of the Menses will hence appear capable of occasioning Strangulations, Belching, Colicks, Stomach-aches, and even Convulsions in the Extremities may be owing to such Obstructions, or to any violent Irrita­tions of the Stomach or Guts. With a View to these Communications, I have frequently applied Vesicatories from the Ears to the Cla­vicles of Children labouring under the Tussis convulsiva with observable good Success.

The spinal Nerves rise generally by a Num­ber of disgregated Fibres from both the ante­rior and posterior Part of the Medulla spinalis, and soon after form a little Knot or Ganglion where they get on their firm Coats, and are extended into firm Cords. They are distin­guished by Numbers, according to the Verte­brae from between which they come out, the superior of the two Bones forming the Hole thro' which they pass, being the one from which the Number is applied to each Nerve. [Page 59]There are generally said to be thirty Pair of them, seven of which come out between the Vertebrae of the Neck, twelve between those of the Back, five from the Loins, and six from the Os sacrum.

The FIRST CERVICAL Pair of Nerves comes out between the first and second Ver­tebrae of the Neck, and having given Branches to join with the tenth Pair of the Head, the second Cervical and Intercostal, and to serve the Muscles that bend the Neck, it sends its largest Branches backwards to the exten­sor Muscles of the Head and Neck; some of which piercing thro' these Muscles run up on the Occiput to be lost in the Teguments there; and many Fibres of it advance so far forward, as to be connected w [...]th the Fibrillae of the first Branch of the fifth Pair of the Head, and of the Portio Dura of the Auditory Nerve. Hence possibly it is that a Clavus hystericus shall suddenly change from the Fore-head to a violent Pain and Spasm in the Back-part of the Head and Neck.

The SECOND CERVICAL is soon joined by some Branches to the ninth of the Head and Intercostal, and to the first and third of the Neck, then has a large Branch that comes out at the exterior Edge of the Sternomastoideus Muscle, where it joins with the Accessorius of the eighth Pair, and then is distributed to the Platysma Myoides, Teguments of the Side of the Neck and Head, parotid Gland and exter­nal Ear, being connected to the Portio Dura of the Auditory Nerve and to the first cervi­ [...]al. The Remainder of this second Cervi [...]al [...] spent on the Levator scapulae, and the Ex­tensors [Page 60]of the Neck and Head. Generally a large Branch is here sent off to join the Ac­cessorius of the eighth Pair, near the superior Angle of the Scapula.

To the Irritation of the Branches of this Nerve, it probably is, that in an Inflammation of the parotid Gland, the Neck is pain'd as far down as the Clavicle, the Head is drawn towards the Shoulder of the affected Side, and the Chin is turned to the other Side. In open­ing the external Jugular-Vein, no Operator can promise not to touch some of the cutane­ous Branches of this Nerve with the Edge of the Lancet, which occasions a sharp pricking Pain in the mean Time, and a Numness of the Skin near the Orifice for some Time after.

The THIRD PAIR of the Neck passes out between the third and fourth cervical Verte­brae, having immediately a Communication with the second, and sending down a Branch, which being joined by a Branch from the fourth cervical forms the PHRENIC Nerve. This desceding enters the Thorax between the sub­clavian Vein and Artery, and then being re­ceived into a Groove formed for it in the Pericardium, it has its Course along this Cap­sula of the Heart, till it is lost in the middle Part of the Diaphragm. The right Phrenic has a pretty streight Course, but the left one is obliged to make a considerable Turn out­wards, to go over the prominent Part of th [...] Pericardium where the Point of the Heart i [...] lodged. Hence in violent Palpitations of th [...] Heart, a pungent acute Pain is felt near th [...] left Orifice of the Stomach.

The other Branches of the third cervic [...] [Page 61]Nerve are distributed to the Muscles and Te­guments at the inferior Part of the Neck and Top of the Shoulder. No Wonder then that an Inflammation of the Liver or Spleen, an Abscess in the Lungs adhering to the Dia­phragm, or any other Cause capable of irritat­ing the Diaphragm, should be attended with a sharp Pain in the Top of the Shoulder, as well as Wounds, Ulcers, &c. of this Muscle itself. If the Irritation of this Muscle is very violent, it may occasion that convulsive Con­traction of the Diaphragm which is called a Hiccough, and therefore a Hiccough in an In­flammation of the Liver has been justly declar­ed to be an ill Symptom.

The Irritation of the thoracic Nerves so as to produce sneezing, may sometimes free the phrenic Nerves from any Spasm they occasi­on; so that sneezing sometimes takes away the Hiccough, and a Derivation of the Fluid of the Nerves any other way may do the same Thing: Or the Hiccough may also be some­times cured by a Surprize, or any other strong Application of the Mind in thinking or in dis­tinguishing Objects.

The FOURTH CERVICAL Nerve, after sending off that Branch which joins with the third to form the Phrenic, and bestowing Twigs on the Muscles and Glands of the Neck runs to the Arm-Pit, where it meets with the FIFTH, SIXTH and SEVENTH Cervicals' and FIRST DORSAL, that escape in the Interstices of the Musculi scaleni, to come at the Arm-Pit where th [...]y join, sepa­rate, and re-join in a way scarce to be rightly expressed in Words; and after giving several [Page 62]considerable Nerves to the Muscles and Te­guments which cover the Thorax, they divide into several Branches to be distributed to all the Parts of the superior Extremity. Seven of these Branches I shall describe under particu­lar Names.

1. CUTANEUS runs down the Fore-part of the Arm near the Skin to which it gives off Branches, and then divides on the Fore-arm into several Nerves, which supply the Tegu­ments there and on the Palm of the Hand. In opening the Cephalic Vein of the Arm at the ordinary Place, the same Symptoms are pro­duced, as I mentioned to be done in opening the external Jugular-Vein, and by the like Cause, to wit, the hurting a Branch of this cutaneous Nerve with the Lancet.

2. MUSCULO-CUTANEUS or perforans Casserii passes thro' the c [...]raco-brachialis Mus­cle, and, after supplying the biceps flexor cu­biti and brachiaeus internus, is spent on the Te­guments on the out-side of the Fore-arm and Back of the Hand.

3. MUSCULARIS has a spiral Course from the Axilla under the Os humeri, and back­ward to the external Part of that Bone, sup­plying by the Way the extensor Muscles of the Fore-arm, to which it runs between the two brachiaei Muscles, to be chiefly bestow­ed on the Muscles that extend the Wrist and Fingers; some of its Branches going likewise to the Flexors, and others serving the Skin on the out-side of the Fore-arm, the Extremity of it descends along the Radius to the Back of the Hand, in which, and in the back convex Part [Page 63]of the Thumb and three large Fingers it termi­nates.

4. ULNARIS is extended along the In-side of the Arm, to give Nerves to the Muscles that extend the Fore-arm and to the Teguments of the Elbow; towards the lower Part of the Arm it slants a little backward to come at the Groove behind the internal Condyle of the Os humeri, thro' which it runs to the Ulna; in its Course along this Bone it serves the neighbouring Muscles and Teguments; and as it comes near the Wrist, it detaches a Branch obliquely over the Ulna to the Back of the Hand, to be lost in the convex Part of se­veral Fingers. The larger Part of the Nerve goes straight forward to the internal Side of the Os pisiforme of the Wrist; where it sends off a Branch which sinks under the large Ten­dons in the Palm, to go cross to the other Side of the Wrist, serving the musculi lumbricales and interossei, and at last terminating in the short Muscles of the Thumb and Fore-finger. What remains of the ulnar Nerve, after supply­ing the short Muscles of the Little-finger, di­vides into three Branches; whereof two are ex­tended along the Sides of the Sheath of the Tendons of the Flexors of the Little-finger, to furnish the concave Side of that Finger; and the third Branch is disposed in the same Way upon the Side of the Ring-finger next to the Little finger.

When we lean or press on the inter­nal Condyle of the Os humeri, the Num­ness and Prickling we frequently feel point out the Course of this Nerve; I have seen a Weakness and Atrophy in the Parts which I [Page 64]mentioned this Nerve to be sent to, after a Wound in the internal inferior Part of the Arm.

5. RADIALIS accompanies the humeral Artery to the bending of the Elbow, serving the Flexors of the Cubit in its Way; then, af­ter giving large Nerves to the Muscles on the Fore-part of the Fore-arm, it continues its Course near to the Radius, bestowing Branches on the circumjacent Muscles. Near the Wrist it gives off a Nerve which is distributed to the Back of the Hand, and the convex Part of the Thumb, and several of the Fingers. The larger Part of this Nerve passing behind the an­nular Ligament of the Wrist gives Nerves to the short Muscles of the Thumb, and after­wards sends a Branch along each Side of the Sheath of the Tendons of the Flexors of the Thumb, Fore-finger, Middle-finger, and one Branch to the Side of the Ring-finger next to the Middle, to be lost on the concave Side of those Fingers.

The Manner of these Nerves of the Fingers, both from the Ulnar and Radial going off, is that a single Branch is sent from the Trunk to the Side of the Thumb and Little-finger far­thest from the other Fingers; and all the rest are supplied by a Trunk of a Nerve, which splits into two some way before it comes as far as the End of the Metacarpus, to run along the Sides of different Fingers that are nearest to each other.

It might have been observed, that in describ­ing the posterior Branches of the ulnar and ra­dial Nerve, I did not mention the particular Fingers, to the convex Part of which, they were [Page 65]distributed. My Reason for this Omission is the Uncertainty of their Distribution; for tho' sometimes these posterior Branches go to the same Fingers, to the concave Part of which their anterior Branches are sent, yet frequent­ly they are distributed otherwise, and I ought to observe that the muscular Nerve has not always that Termination in the Back of the Hand which I mentioned.

6. ARTICULARIS sinks downwards at the Axilla, to get below the Neck of the supe­rior Head of the Os humeri, and to mount a­gain at the Back-part of it; so that it almost surrounds the Articulation, and is distributed to the Muscles that draw the Arm back and raise it up.

7. SCAPULARIS runs straight to the Ca­vitas semilunata of the upper Costa of the Sca­pula, which is made a Hole in the recent Sub­ject, a Ligament being extended from one Angle of the Bone to the other, giving Nerves in its Way to the Muscles of the Scapula. When it has passed this Hole it supplies the Su­praspinatus Muscle, and then descending at the anterior Root of the Spine of the Scapula, it is lost in the other Muscles that lye on the Dor­sum of the Scapula.

The Situation of these brachial Nerves in the Axilla, may let us see how a Weakness and Atrophy may be brought on the Arms by long continued Pressure of Crutches, or such other hard Substances on this Part; and the Course of them from the Neck to the Arm may teach us how much better Effects, Vesicatories or stimulating nervous Medicines would have, when applied to the Skin, covering the trans­verse [Page 66]Processes of the Vertebrae, or at the Axilla, than when they are put between the Shoulders, or upon the spinal Processes in Convulsions or Palsies of the superior Extremities, where a Stimulus is required.

The TWELVE DORSAL Nerves of each Side as soon as they escape from between the Vertebrae, send a Branch forward to join the In­tercostal, by which a Communication is made among them all, and they soon likewise give Branches backwards to the Muscles that raise the Trunk of the Body, their principal Trunk being extended outwards to come at the Fur­row in the lower Edge of each Rib, in which they run toward the anterior Part of the Tho­rax, between the internal and external interco­stal Muscles, giving off Branches in their Course to the Muscles and Teguments of the Thorax.

The FIRST Dorsal has already been said to have this Particular in it, that it contributes to form the brachial Nerves, and that the two Branches of the Intercostal, which come down to the Thorax, form a considerable Ganglion with it.

The SIX inferior dorsal Nerves give Bran­ches to the Diaphragm and abdominal Mu­scles.

The TWELFTH joins with the first Lum­bar, and bestows Nerves on the Musculus qua­dratus Lumborum and Iliacus internus.

May not the Communications of all these Nerves be one Reason of the Parts they serve acting so uniformly and conjunctly in Respi­ration, and conspiring together in the convul­sive Motions of Coughing, Sneezing, &c? [Page 67]The twitching Spasms that happen sometimes in different Parts of the Muscles of the Abdo­men, by any Irritation on the Branches of the lower dorsal Nerves are in Danger of occa­sioning a Mistake in Practice, by their Resem­blance to the Colick, Nephritis, &c. The Communications of these lower ones with the Intercostals may serve to explain the violent Effort of the abdominal Muscles in a Tenes­mus and in Child-bearing.

As the Intercostal is so much larger in the Thorax than any where else, and seems to di­minish gradually as it ascends and descends, there is some Suspicion that the Trunk of it is here, from which the superior and inferior Parts are sent as Branches.

The FIVE LUMBAR Nerves on each Side communicate with the Intercostal and with each other, and give posterior Branches to the Loins.

The FIRST commuicates with the last dor­sal, sends Branches to the abdominal Muscles, to the Psoas and Iliacus, and to the Teguments and Muscles on the anterior Part of the Thigh; while its principal Branch joins with other Nerves to form the crural Nerve.

The SECOND LUMBAR Nerve passes through the Psoas Muscle, and is distributed nearly in the same Way as the former, as is also the THIRD.

Branches of the first, second and third make up one Trunk, which runs along the anterior Part of the Pelvis, and passing in the Notch at the anterior Part of the great Hole common to the Os Pubis and Ischium, is spent on the Ad­ductor Muscles and the Teguments on the In­side [Page 68]of the Thigh. This Nerve is called the OBTURATOR or POSTERIOR CRURAL NERVE.

By united Branches from the first, second, third and fourth lumbar Nerves, a Nerve is formed that runs along the Psoas Muscle, to escape with the external Iliac Vessels out of the Abdomen, below the tendinous Arcade of the external oblique Muscle. This Nerve, which is named the ANTERIOR CRURAL, is distributed principally to the Muscles and Teguments on the anterior Part of the Thigh. A Branch however of this Nerve runs down the Inside of the Leg to the superior Part of the Foot keeping near to the Vena, saphaena; in opening of which with a Lancet at the Ancle, the Nerve is sometimes hurt, and occasions sharp Pain at the Time of the Operation, and Numness afterwards.

The Remainder of the fourth Lumbar and the fifth joins in composing the largest Nerve of the Body, which is soon to be described.

Whoever attends to the Course of these lumbar Nerves, and of the spermatic Vessels and Nerves upon the Psoas Muscle with the oblique Passage of the Ureter over that Muscle, will not be surprized, that when a Stone is passing in this Canal, or even when it is in­flamed, the Trunk of the Body cannot be raised erect without great Pain; or that the Skin of the Thigh becomes more insensible, and the Thigh is drawn forward, and that the Testicle often is drawn convulsively towards the Ring of the abdominal Muscles.

The SIX PAIR of the OS SACRUM consist each of small posterior Branches sent [Page 69]to the Hips, and of large anterior Branches.

The first, second and third, after coming through the three superior Holes of the Os sa­crum, join together and with the fourth and fifth of the Loins, to form the largest Nerve by much of the Body, which is well known by the Name of SCIATIC or ISCHIATIC Nerve: This, after sending large Nerves to the different Parts of the Pelvis, and to the external Parts of Generation and the Podex, as also to the Muscles of the Hips, passes behind the great Tuber of the Os Ischium, and then o­ver the Quadrigemini Muscles to run down near to the Bone of the Thigh at its posterior Part, giving off Nerves to the neighbouring Muscles and Teguments. Some Way above the Ham, where it has the Name of the Popli­taeus Nerve, it sends off a large Branch that passes over the Fibula, and sinking in among the Muscles on the anterior external Part of the Leg, runs down to the Foot, to be lost in the superior Part of the larger Toes, supplying the neighbouring Muscles and Teguments e­very where in its Passage. The larger Branch of the Sciatic, after giving Branches to the Mu­scles and Teguments about the Ham and Knee, and sending a large cutaneous Nerve down the Calf of the Leg, to be lost at last in the exteri­or Side of the Foot and superior Part of the lesser Toes, sinks below the Gemellus Muscle, and distributes Nerves to the Muscles on the Back of the Leg; among which it continues its Course, till passing behind the internal Mal­leolus and in the internal Hollow of the Os Calcis, it divides into the two plantar Nerves. The internal of which is distributed to the [Page 70]Toes, in the same Manner as the radial Nerve of the Hand serves the concave Side of the Thumb and Fingers, and the external Plantar is divided and distributed to the Sole of the Foot and Toes, nearly as the ulnar Nerve is in the Palm of the Hand and in the concave Part of the Fingers.

By applying what was said of the Nerves in general to the particular Distribution of the Nerves of the inferior Extremities, we may see how People with fractured Legs, especial­ly where there are Splinters, should be so sub­ject to convulsive Startings of the fractured Member, and why upon tying the Blood-ves­sels in an Amputation of the Leg, the Patients should sometimes complain of violent Pain in their Toes; why such Patients should also be troubled with Startings, or why, for a con­siderable Time after the Amputation of the diseased Limb, when the Suppuration is well advanced, they should complain of Pain in the Sore which occasioned the Amputation.

The FOURTH Nerve of the Os sacrum, which with the two following is much smal­ler than the three superior, soon is lost in the Vesica urinaria and Intestinum rectum.

The FIFTH comes forward between the Extremity of the Os sacrum and Coccygis, to be distributed principally to the Levatores Ani.

The SIXTH advances forward below the broad Shoulders of the first Bone of the Os Coc­cygis, and is lost in the Sphincter Ani and Te­guments covering it.

The Branches of the four last cervical Nerves, and of the first dorsal, which are be­stowed on the superior Extremity, and the two [Page 71]Crurals, with the Sciatic, which are distribu­ted to the inferior Extremities, are much larger proportionally to the Parts they serve, than the Nerves of the Trunk of the Body, and espe­cially of the Viscera are; and for a very good Reason, that in the most common necessary Actions of Life a sufficient Quantity of Fluid, on which the Influence of Nerves seems to depend, may be supplied to the Muscles there, which are obliged to perform so frequent and violent Contractions. The Size of the Nerves of the inferior Extremities seems larger pro­portionally than in the superior Extremities; the inferior Extremities having the Weight of the whole Body to sustain, and that frequently at a great Disadvantage. What the Effect is of the Nerves here being lesed, we see daily, when People happen by sitting wrong to com­press the sciatic Nerve, they are incapable for some time after to support themselves on the affected Extremity; and this is still more re­makeable in the Sciatic or Hip-Gout, in which the Member is not only weakned, but gra­dually shrivels and wastes.