Chap. IV. The Anatomy of a HOKS^. 39 



Sutfftance of a Nerve, which is very folid and compafl', 

 proceeding by a Sort of Gradation frorn that of the Brain ; 

 for as the Corpus Callofum^ or inner Subftance of the Brain, 

 is more firm than the Cortical Part, fo a Nerve is even at its 

 Origin fome Degrees beyond that in Solidity ; by vv'hich 

 Means it is the more adapted to its peculiar Funftions. But 

 befides the Solidity and Compadlnels of the Nerves, their 

 Tenfenefs is alfo a great Means of their Adion ; for as the 

 Blood-veflels, which have no other Senfe but what is bor- 

 rbvv'ed from them, and as their Office is only to carry vita! 

 Spirits for the common Nourifliment of the Body ; as thefe 

 are therefore branched off in many Circumvolutions and 

 Turnings, and are form'd irregularly in fuch Meanders as 

 we obferve in Brooks and Rivulets : And as fome Branches 

 are feni upwards, and others downwards, as is neceflary, in 

 order to their feveral Functions ; fo the Nerves, on the other 

 Hand, as they take their Origin from the Head and Spine, 

 are detach'd from thence into all Parts of the Body in fuch 

 manner, as they may be every where braced as ftreight as 

 the Strings or Cords of an Inftrument ; by which Means 

 they have a free and uninterrupted Undulation, and as in 

 all their Branchings, they are little or no ways contorted, 

 but for the moll Part form compleat and perfect Angles, 

 the faid Undiilation is communicated as entirely to their 

 Origin, as if their Courfe was directly ftreight from it. 



And therefore as the Nerves are of a very compacfl and 

 folid Form, and can be braced and extended in fuch Man- 

 ner as has been obferved, and confequentiy endued with 

 Elafticity, they muft eafily and fuddenly communicate 

 all Senfations to the Imagination, there being no Part of 

 the Body which does not participate of fome little Fihilla 

 or Threads detached from them j or, according to fome, 

 there being no Part of the Body, which is not more or lefs 

 adapted to receive the nervous Juice ; by which Means a 

 clofe and intimate Correfpondence is kept up with the 

 Nerves j fo that whenever an animal Body is touched on 

 any Part, it is prefently fenfible of that Touch, by virtue 

 of the Communication which they keep between the Head 

 and all Parts of the Body. 



Now as to Motioo, to which the Nerves are equally 

 fubfervient, that (I think) is termed Voluntary in a Man, 

 and Spontaneous in a brute Creature, as the one is faid to 

 ad by the Determination of the IVill^ and the other by In- 

 ii'in^ i but this is not material, fiuqs both are laid 10 be pro- 

 D \ duccd 



