Page:Cyclopaedia, Chambers - Volume 2.djvu/276

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NER

NEPHRITICTJS JUp«, a precious Stone, fo call'd from its extraordinary Virtues againft the Stone and Gravel in the Kidneys. See Stonk.

'Tis a kind of Jafper, of a greyifh Colour, mix'd with a little blue, fometimes white and black 5 and only differs from Jafper, in its being harder, and always without any thing of red.

'Tis brought chiefly from New Spain, where it is fome- times found in Pieces large enough to make moderate Gups. There is fome likewife found in OldSpam and Bohemia.

This Stone is very dear, by reafon of the wonderful Vir- tues afcribed to it. A Cup made of it was fold for 1600 Crowns in the time of the Emperor Rudolphus II.

The beft for Medicinal Ule is of a blui/h grey, fat and unctuous, as Talc of Venice.

The Indians of New Spain, who firft difcover'd its ufe, and taught it the Europeans, wear it hung about their Neck, after having cut it in various Figures, chiefly Beaks of Birds : Whence fome Charletans take occafion to counterfeit it, by cutting Jada, and other Stones, into like Figures 5 and fell it at great Prices to thofe who have an Opinion of its Ne- phritic Faculty.

NEPOTISM, aTermufed mltaly, in fpeaking of the Authority which the Pope's Nephews, i. e. his Baftards, have in the Administration of Aftairs, and in the Care the Popes take to raife and enrich them.

Many of the Popes have endeavoured to reform the Abufes of Nepotifm, but hitherto in vain. J-eti has wrote exprefly on the Subject, 11 Nepotifmo.

NEPTUNALIA, Feafts held among the Antients in honour of Neptune.

The Neptunalia differ'd from the Confualia, in that the latter were Feafts of Neptune, confider'd as prefiding over Horfesand the Manage. See Consualia.

Wheteas the former were Feafts or" Neptune in the general, and not confider'd under any particular Quality. They were celebrated on the 10th of the Calends of Auguft.

NEREIDS, or Nereides, Fabulous Deities of the An- tients, fuppofed to inhabit the Sea. See God.

The Nereids were fifty in number j all the Sons of Nep- tune by the Nymph Doris. Their Name and Genealogies aredefcribed by Hefiod.

NERVE, in Anatomy, a round, white, long Body, like a Cord, compofed of fevetal Threads, or Fibres ; deriving its Origin from the Brain, or the Spinal Marrow ; and di- ftributed throughout all the Parts of the Body ; ferving for the Conveyance of a Juice call'd Animal Spirits, for the performance of Senfation and Motion. Sec Sensation, Muscular Motion, ti?c.

For the Origin of the Nerves: From every Point of the Cortex of the Brain, there arife minute medullary Fibres 5 which, in their Progrefs uniting together, at length be- come fenfible, and thus constitute the Medulla of the Brain, and the Spine. See Cortex, Medulla, &c.

Hence they are continued, and in their farther Progrefs, become diftinguifll'd or feparated by Coats which are de- tach'd to them from the Dura and Pia Mater, into feveral diftinct Fafciculi, ot'Nervesj refembling, in the Pofltion of their compone.ntFibrill<e, fo many Horfes Tails.wrapp'd up in a double Tunic. See Fibre.

'Tis probable that the medullary Fibres of the Cere- helium, rifingup towards the fore-parts of the Medulla Obion- £ata, do, part of them, join the Nerves arifing thence, but fo as flill to retain their different Origin, Progrefs, and Fun- ctions. The reft of the Fibres of the Cerebellum are fo mix'd with thofe of the Brain, as that there is, perhaps, no part of thewhole Medulla Oblongata,*)* Spinalis,v/hcrc there are not found Fibres of each kind ; and thus, to confiitute the Body of each Nerve, both kinds of Fibres contribute ; tho the end and effect of each bequite different. See Cerebel,^.

The Nerves thus form'd, and fent from the Medulla Ob- longata and Spinalis while within the Cranium, are ten Fair 5 thovery improperly fo accounted j inafmuch as moll of them do in reality confift of feveral diftinct, very large Nerves.

From the Spinal Marrow, continued without the Cra- nium, there arife, after the like manner, thirty Pair, to which may be added another Pair fent from the Vertehr/e of the Neck, augmented in its Progrefs by Branches from the fecond and third Pair, and at laft join'd to the eighth Pair.

All thefe, while within the Medulla, are pulpous ; as foon as they quit it, they acquire a Sheath, or Cafe, wherewith being defended, they proceed to the Dura Mater, which is perforated into an open Vagina, reaching as far as the Fora- mina of thoCranium, dellin'd for the tranfmiflion of Nerves ; where the nine firft Pair, and the Acceffhry Pair, affuming this Vagina, or Cafe, pafs fafelyourof the Cranium.

Theother thirty and one Pair defcend thro' Spaces be- tween the Commiffures of the Apophyfes of the Vertebra ; whence, firm, hard, and well cloath'd as they are, they aredifperfed thro' all, even the fmalleft Points of the folid Parts of the Body yet known. See Solid.

■ The, ",'• or Covers of the f>= Nm*» are every where mvefted with Blood-Veffels,Lymphatics, and otherVeficles of a very tight lexture, which ferve to collect, strengthen, and contrast thefthnlU ; and from which many of the Phe- nomena of theNerves, and of Difeafes, ate accountable.

As foon as the laft Extremities of the Nerve, are about to enter the Parts to which they belong, they again lay afide their Coats, and become expanded either into a kind of thin Memlranula, or into a foft Pulp. See Membrane and Flesh.

Now, upon confidering firft, That the whole vafcular Medulla of the Brain goes to the conftjtuting of the Fi- bril!* of the Nerves ; nay, is wholly continued into, and ends in them ; Secondly, That upon eoinpreffion, teating difperfion, putrefaction, tfc. of the Medulla of the Brain all the Ailions ufed to be perform'd by the Nerves ariiino thence, are immediately abolilhed, even tho the Nerves con- tinue entire and untouch'd ; Thirdly, That the Nerves themfelves are every where found lax, pendulous, crooked retrograde, and oblique, yet effect Motion and Senfation almolt inftaptaneoufly ; Fourthly, That when clofu bound or comprefs'd, tho in all other relpecls entire, they lofc all their Faculty in ihofe Parts between the Liaature and tho Extremes to which they tend, without lofing~any in thofe Parts between the Ligature and the Medulla of the Brain or Cerebellum: it evidently appears, that the nervous Fi- br:lU do continually take up a Humour or Juice from tho Medulla of the Brain, and rranfmit it by fo many diftinct Canals to every Point of the whole Body ; and by means hereof alone perform all their Funftions in Senfation, Muf- cular Motion, Sgfc. See Sensation and Muscle.

Which Humour is what we popularly call Animal Spirits or the Nervous" Juice. See Animal Spirit.

Nor does there appear any Probability in that Opinion maintain d by fome ; viz. That the Nerves perform all their Aflion by the Vibration of a tenfe Fibrilla ; which is inconfiftent with the nature of 1 foft, pulpous, flaccid crooked, wavy Nerve, and with that nice dil:inctn<-fs wherewith the Objefts of our Senfes are represented and Mufcular Motions perform'd.

Now, after the fame manner as the Atterial Blood is perpetually earned into all tho Parts of the Body furnilh'd with thofe Veffels ; fo we conceive a Juice pre- paid in the Cortex of the Brain and Cerebellum, convey'd thence every Moment thro" the Nerves to every Point of the folid Body. The fmallnefs of the Veffels in the Cor- tex, as exhibited in Ruyfch's InjeSions, which yet are only Arterious, and therefore incredibly thicker than the laft Emiffary derived thence, /hew how flender thefe hollow Nervous Stamina muft be. But the grear Bulk of the Brain compared with the exceeding Smallnefs of each Fibrilla fhews, that their number muft be great beyond the limits of all Imagination.

And again, the great Quantity of Juice conftantly brought hither, and violently agitated, will occafion a conftant Ple- nitude, Opennefs, and Action of thefe little Canals.

But, as ftefll Juice is every moment prepared, and the laft is continually ptotruding the former ; as foon as it has done its laft Office, it feems to be driven out of the laft Filaments into the fmalleft Lymphatic Verntlx, both about the Glands, and elfewhere 5 thence into the Lymphatics fomewhat latger; and again from thefe to the common Lymphatic Veffels with the Valves of Veins, and at length into the Veins and the Heart ; and thus like the other Juices of the Body, does it make its Citcuit round ihe Body. See Circulation of the Spirits.

Upon the whole, if ws confider the great Bulk of the Brain, Cerebellum, Medulla Oblongata, and Medulla Spinalis with regard to the Bulk of the reft of the Solids of the Body ; the great number of Nerves distributed hence throughout the whole Body j that the Brain and Carina, that is the Spinal Matrow, are the Balis in an Em- bryo, whence, according to the great Malpighi, the other parts are aftetwards form'd ; andlaftly, that there is fcatce any part of a Body, but what feels or moves 5 it will ap- pear very probable, that all the folid parts of the Body are wove out of nervous Fibres, and confift whollyof 'em. See Stamen.

The Antients only allow'd of feven Fairs or Conjugations of Nerves, proceeding from the Brain ; which, with their Functions, they comprifed in thefs wo Latin Verfes :

Optica prima, oculos movet altera, tenia guflat,

Qusirtaq; quinta audit, vagafexta eft, feptima lingua.

But the Moderns, as before obferv'd, reckon ten, which arc as follow.

Nerves of the Brain, or Cerebrum.

OlfaBory Nerves, Far Olfaflorium, or the Olfactory Pair

arifes in the fore-part of the Brain, juft below the 0)

Frontis ; thefe being pretty thick near the Os Cribrofum, ar e

7 U ther.