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 Part VI. ANATOMY. 253 facrum and coccygis, to be diftributed principally form the larged nerve of the body, which is well known tothetheos levatores ani. by the name of Sciatic or Ischiatic nerve : This, The Sixth, which fome think to be only a produftfon after fending large nerves to the different parts of the of the dura mater, advances forward below the broad pelvis, and to the external parts of generation, and the ftioulders of the firft bone of the os coccygis, and is loft: podex, as aifo to the mufcles of the hips, paffes behind the fphintter ani and teguments covering it. the great tuber of the os ifchium, and then over the in The fize of the nerves of the inferior extremities feeins quadrigemini mufcles, to run down near to the bone of larger proportionally in the fuperior extremities; the thigh at its back-part, giving off nerves to the neigh- inferior extremitiesthanhaving the weight of the whole bouring mufcles and teguments. Some way above the the to fuftain, and that frequently at a great difadvanham, where it has the name of the poplitaut nerve, it body tage. What the effedt is of the nerves here being infends off a large branch that paffes over the fibula, and jured, we fee daily, when people happen, by fitting wrong, finking in among the mufcles on the anterior external part to comprefs fciatic nerve, they are incapable for fome of the leg, runs down to the foot, to be loft in the up- time after tothefupport themfelves on the affedted extreper part of the larger toes, fupplying the neighbouring mity ; and this is ftill more remarkable in the fciatic or mufcles and teguments every where in its paffage. The hip-gout, in which the member larger branch of the fciatic, after giving branches to the but gradually (hrivels and waftes. is not only weakened, mufcles and teguments about the ham and knee, and fending a large cutaneous nerve down the calf of the leg, Uses of the Nerves. to be loft at laft on the outfide of the foot and upper part of the leffer toes, finks below the gemellus mufcle, and Many experiments concur in proving, that the nerYes diftributes nerves to the mufcles on the back of the leg; are the inftruments of fenfation. As to the mode of their among which it continues its courfe, till paffmg behind operation, feveral different theories have been given. Some the internal malleolus, and in the internal hollow of the fuppofe, that they are elaftic cords, refembling fiddleos calcis, it divides into the two plantar nerves : The in- ftrings ; and that they convey fenfations to the brain by ternal of which is diftributed to the toes, in the fame a kind of vibratory motion. Others have fuppdfed them manner that the radial nerve of the hand ferves the con- to be tubular, and to contain a fluid called animalfpirits ; cave fide of the thumb and fingers; and the external and that fenfation is produced by the motions and counplantar is divided and diftributed to the foie of the foot ter-motions of this fluid. Many ufelefs volumes have been and toes, nearly as the ulnar nerve is in the palm of the wrote upon each of thefe hypothefes.—Another and more hand, and in the concave part of the fingers. recent theory fuppofes, that the nerves are not tubular, Several branches of thefe nerves, that ferve the infe- but that they are pervaded by a fubtile elaftic fluid called rior extremities, pierce through mufcles. /Ether; and that lenfation, fee. are occafioned by the ofThe Fourth, which, with the two following, is cillations of that fluid. A few detached and ill-digefted much fmailer than the three fuperior, foon is loft in the feraps of this theory have already appeared in fome temvefica urinaria and inteftinum re&um. porary productions, the principal of which has been fuffiThe Fifth comes forward between the extremity of ciently animadverted upon under the word ./Ether. E X P L A N,A T I O N of PLATE XVIII. Fig. 1. Reprefents the inferior part of the brain;— 4 4, The fourth pair, named pathetic,—-which is the anterior part of the whole fpine, including the wholly fpent upon the mufculus trochlearis of the eye. medulla fpinalis;—with the origin and large portions 5 5, The fifth pair divides into three branches.—The of all the Nerves. named ophthalmic, goes to the orbit, fupplieS A A, The anterior lobes of the cerebrum. B B, The firft, the lachrymal gland, fends branches out to the forelateral lobes of the cerebrum. C C, The two lobes head and nofe.—The fecond, named fuperior maxilof the perebellum. D, Tuber annulare. E, The paffupplies the teeth of the upper jaw, and fome fage from the third ventricle to the infundibulum. lary, of the mufcles the lips.—The third, named infeF, The medulla oblongata, which fends off the me- rior maxillary, ofis fpent mufcles and teeth of dulla fpinalis through the fpine. G G, That part of the lower jaw, tongue,uponandthemufcles the os occipitis which is placed above (H H), the 6 6, The fixth pair, which, after fendingofoffthethelips. bethe tranfverfe proceffes of the firft cervical vertebra, ginning of the intercoftal or great fympathetic, is fpent I I, &c. The feven cervical vertebras, with their in- upon the abduftor oculi. 7 7, The feventh pair, natermediate cartilages. K K, &c. The twelve dorfal auditory, divides into two branches.-—The lafvertebrae^ with their intermediate cartilages. L L, &c. ' wed ea named portio mollis, is fpent upon the internal The five lumbar vertebrae, with their intermediate car- geft, y-—The fmalleft, portio joins branch to the from fifth tilages, M, The os facrum. N, The os coccygis. •pair within the ear bydura, a reflected Nerves.—i i, The firft pair of nerves, named the fecond of internal the fifth, and within the tympanum, clfaetory, which go to the nole. 2 2, The fecond by a branch from the tbirefof the fifth, named chorda pair, named optic, which goes to form the tunica re- tyvipani.—Vid. fig. 3. near B. 8 8, &e. The eighth tina of the eye. 3 3, The third pair, named vwtor pair, named par vagum,— which accompanies the inocttli; it fupplies moil of the mufcles of the eye-ball. tercoftal, and is fpent upon the tongue, larynx,‘ phaVol. I. No. 11. 3