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248 ANA T o M Y. ' Part V. the optic nerve, or in thofe who had one of their eyes Sect, II. Of the particular Nerves. taken out, make it appear, that there is no fuch intimate It is generally faid, that there are forty pair of union of fubltance; the optic nerve of the affected fide nerves in all; of which ten come out from the encepha- only being wafted, while the other was large and plump. lon, and the other thirty have their origin from the And the fame oblervations are contradictory to the docfpinal marrow.
trine of a decuffation of all the nerves, for the difeafe Of the ten pair of nerves which come from the ence- could be traced from the affeCted eye to the origin of the phalon, the firji is the Olfactory, which have their -.nerve on the fame fide. origin from the corpora ftriata, near the part where the Thefe people whofe optic nerves were not joined, hainternal carotid arteries are alrout to fend off their branches ving neither feen objects double, nor turned their eyes to the different parts of the brain; and in their courfe different ways, is alfo a plain proof, that the conjundion under the anterior lobes of the brain, which have each a of the optic nerves will not ferve to account for either depreffion made for lodging them, become larger, till the uniform motions of our eyes, or our feeing objeds they are extended to the cribriform bone; where they Angle with two eyes. fplit into a great number of fmall filaments, to pafs The retina of a recent eye, without any preparation, through the little holes in that bone; and being joined appears a very fine web, with fom.e blood-veffels coming by a branch of the fifth pair of nerves, are fpread on the from its center to be dillributed on it; but, after a good injection of the arteries that run in the fubftance of this membrane of the nofe. The tender ftrudlure and hidden expahfion of thefe nerve, as is common to other nerves, it is with difficulnerves on fuch a large furface, render it impoflible to ty that we can obfe'rve its nervous medullary fubftance. trace them far; which has made fome authors deny them —The fituation of thefe vefl’els in the central part of the to be nerves: But when we break the circumference of optic nerve, the want of medullary fibres here, and the the cribriform lamella, and'then gently raifeit, we may firmnefs of this nerve before it is expanded at its entry fee the diflribution of the nerves fome way on the mem- into the ball of the eye, may be the reafon why we do not fee fuch bodies, or parts qf bodies, whofe picture brane of the nofe. The contrivance of defending thefe long foft nerves falls on this central part of the retina. from being too much prefled by the anterior lobes of the The Third Pair rife from the anterior part of the brain under which they lie, is Angular; becaufe they proceffus annularis, and piercing the dura mater a little have not only the prominent orbitar procefles of the before, and to a fide of tjie ends of the pofterior clinoid of the fphenoid bone, run along the receptacula, frontal bone to fupport the brain on each fide, with the orprocefs finufes, at the fide of the ephippium, to veins going into the longitudinal finus, and other at- getcavernous tachments bearing it up, but there is a groove formed in out at the foramina lacera; after which each oHhera each lobe of the brain itfelf for them to lodge in •—Their divides into branches, of which one, after forming a fplitting into fo many fmall branches before they enter little ganglion, is diftributed to the globe of the eye; the are fent to the mufculus reCtus of the palpebra, the bones of the flail 1, is likewife peculiar to them ; for others the attollens, adduCtor, deprimens, and obliquus generally the nerves come from the brain in difgregated and tomufcles of the eye-ball. Thefe mufcles bsjng princifilaments, and unite into cords, as they are going out at minor pal inftruments in the motions of the eye-lid and eye-ball, the holes of the bones. This contrivance is the bell for this anfwering the purpofe they are defigned for, of being the culi.nerve has therefore got the name of the Motor Oorgan of finelling; for had they been expanded upon the The Fourth Pair, which are,the fmalleft nerves of membrane of the nofe into a medullary web, fuch as the any, derive their origin from the back-part of thebafe of optic nerve forms, it would have been too fenfible to the teftes; and then making a long courfe on the fide of bear the impreflions of fuch objects-as are applied to the the protuberance enter the dura mater a little farnofe; and a diftribution in the more common way, of a annular back, and more externally than thethirdpart, to run cord fending off branches, would not have been equal ther alfo along the receptacula, to pafs out at the foramina laenough for fuch an organ of fenfation. be entirely fpent on the mufculi trochleares, The fecond pair of nerves, the Optic, rifing from ~ cera, and to oblique mufcles of the eyes. Thefe mufthe thalami nervorum opticorum, make a large curve out- or fuperior being employed in performing the rotatory motions, wards, and then run obliquely inwards and forwards, cles riil they unite at the fore-part of the fella Turcica; then and the advancement of the eye-balls forward, by feveral of our paflions are expreffed, the nerves foon divide, and each runs obliquely forwards and out- which them have got the name of Pathetici. wards to go out at its proper hole in the fphenoid bone, thatTheferve Pair are large nerves, riling from the accompanied with the ocular artery, to be extended to annular Fifth procefles where the medullary procefles of the the globe of the eye, within which each is expanded into cerebellum join in the formation of that tuber, wo enter a very fine cuplike web, that lines all the infide of the the dura mater the point of the petrous proceft of the eve as far forwards as the ciliary circle, and is univer- temporal bonesnear
- and ffien finking clofeby the receptacula
fally known by the name of Retina. the fides of the fella turcica, each becomes in appearance Though the fubftance of this pair of nerves feems to atthicker, and goes out of theikull in three great branches. be blended at the place where they are joined; yet ob- The y?r/? branch of the fifth'the Ophthalmic, fervations of people whofe optic nerves were not joined, orbit, and of others who were blind of one eye from a fault in which runs through the foramen laceruci, to the having
