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it thirty. The gadi, and fome other fifti have thirty ; and the coregones and falmons, at leaft fixty of them. The clupea or thrifla of authors has at leaft eighty of them ; and the fword-fifti, the tunny, the mackrel, and many others, have more than a hundred of them, or have them indeed without number. Their differences in figure are alfo very great. In fome fifh they are long and narrow, as in the fal- mons, gadi, and clupcie. In others, they are very ftiort and thick, as in the pleuronecti, and ofmerus. In the great- eft part of fifties they are much fmaller than the reft of the guts; but in the mullet and fand-eel they are nearly as large as the Inteftine itfelf; It is remarkable, that thefe appen- dices to the pylorus, or Inteftine, are not only found in fifties, but in fome infects. Dr. Tyfon found three or four of them in that fpecies of infect called the blatta. Jrtedi's Ichthy- ology. See the article Blatta.
INTRADA, in the Italian mufic, is ufed to denote an entry, and is much the fame as prelude, or overture. See the articles Prelude, and Overture, Cyd.
INTRENCHMENT, in the art of war, all forts of works made to fortify a poll:, againft an enemy. See the article Retrenchment, Cyd.
It was a maxim amongft the Romans, that even in their moft hafty marches they intrenched every night.
INTRITA, a name given by fome authors to the maltha, a liquid bitumen ufed by the antients inftead of mortar in building. See the article Maltha.
INTRODUCTOR, in antiquity, was particularly ufed for an officer, who introduced the Athlete to the Stadium, or place where they were to contend.
INTRUSIONE, a writ brought againft an Intruder, by him that hath fee-fimple, fcfe. New Nat. Brit. 453. Blount, Cowel.
INVADIATUS, in our old writers, a perfon accufed of any crime* which not being fully proved,- he was put fob debita fide jujftone, and called Invadiatus. Blount.
INVECTIVE, in rhetoric, differs from reproof, as the latter proceeds from a friend and is intended for the good of the perfon reproved ; whereas invetfive is the work of an enemy, and entirely defigned to vex and give uneafmefs to the per- fon againft whom it is directed. Vojf. Rhet. L. 3. p. 420.
INVOLUCRUM, among botanifts, exprefles that fort of cup which furrounds a number of flowers together, every one of which has befide this general cup its own particular pe- rianthium. The Involucrunt confifts of a multitude of little leaves difpofed in a radiated manner. See the article Calyx.
JOA Mufchata, in botany, a name ufed by fome authors for the chamxpitys or ground-pine. Ger. Emac. Ind. 2.
JOHNSWORT, or St. John's-wort, Hypericum, in bo- tany, &c. See the article Hypericum.
JOINTS (Cyd.)— The fupplenefs that the Joints may be brought to by long practice from the time of infancy, is furprifing. Every common pofture-m after at a country-fair fliews us a great deal of this ; but the moft wonderful inftancc we have ever had of it, was in the perfon famous in London fifty or fixty years ago, whofe name was Clark, and com- monly called Clark the pofture-mafter. This man had found the way by long practice to diftort many of the bones, which no body before had ever thought it practicable to alter the pofition of; and had fuch an abfolutc command of his mufcles and Joints, that he could almoft disjoint his whole body ; fo that he once impofed on the famous Mul- lens by his diftortions, fo far that he refufed to undertake his cure, as fuppofing him beyond relief. But, to his amaze- ment, he had no fooner given him over, than the man re- ftored himfelf to the figure and condition of a proper man, with no distortion about him. See Phil. Tranf, N° 242. p. 262.
Joint 'Cartilage, or A^TICVIATIIUQ-Cartilage. An articu- lating cartilage is an elaftic fubftance, uniformly compact, of a white colour and fomewhat diaphanous, having a fmooth poliftied furface covered with a membrane, harder and more brittle than a ligament ; but fofter and more pliable than a bone. Philof. Tranf. N° 469. p. 515. "When a Joint-cartilage is well prepared by the anatomift, it feels foft, and yields to the touch ; but, as foon as the pref- fure is taken off, reftores itfelf to its former equality of fur- face. Its fuperficies, examined by a glafs, appears like a piece of velvet. If we endeavour to peel off the matter of the cartilage in feveral lamellae, we find it impracticable; but if we ufe a certain degree of force, it feparates from the bone in fmall pieces, and we never find the edge of the remaining part oblique, but always perpendicular to the fub- jacent furface of the bone. If we view this edge thro' a microfcope, it appears like the edge of a piece of velvet ; that is, it is feen to be a mafs of fhort and nearly parallel fibres, riling from the bone and terminating at the furface of the cartilage ; and the furface of the bone itfelf is plan'd out into a number of fmall circular dimples in which the bundles of thefe fibres are fixed. Thus we may very aptly compare the fubftance of the cartilage to the pile of velvet, and the furface of the bone to the web of filk which is the bafis of it. In both fubftances the fhort threads or filaments fink in waves
on being prefled, but by the power of elafticiiy they both recover their perpendicular direction as foon as they are no longer fubjecW ib a comprcfling force. Thefe perpendi- cular fibres, doubtlefs, make the greateft part of the fub- ftance of the cartilage in its natural ftate. In the beft pre- parations they leem to make up the whole ; but it is pro- bable, that in the recent ftate there were a number of tranf- verfe fibrils ferving to connect thefe erect ones together, and form the whole into a iblid body ; and that thefe perifti in making the preparation.
We are told by anatomifts, that cartilages are covered with a membrane called perichondrium. If they mean the carti- lages of the ribs, larynx, ear, &c. there indeed fitch a mem- brane is very confpicuous ; but the perichondrium of the fmooth articulating cartilages is fo delicately thin, and fo firmly braced upon the furface, that there is great room to doubt whether it has been rightly underftood, or demon- strated.
This membrane has, however, been raifed by fome late ana- tomifts in pretty large pieces, after macerating, and it is found to be a continuation of that fine fmooth membrane which lines the capfular ligament folded over the end of the bone ; for when that ligament is inferred on the neck of the bone, or between the infertion of the ligament and the border of the cartilage, it is very confpicuous, and may be pulled up with a pair of pincers ; but where it covers the cartilage it is connected fo clofe, that it is not to be traced while recent, without the greateft care and delicacy. In this particular it refemblcs that membrane which is common to the eye-lids and the fore-part of the ball of the eye, and which is loofely connected with the albuginea, but ftrongly attach'd to the cornea. From this defcription it is plain, that every Joint of the human body is invefled with a membrane, which forms a compleat bag, and gives a covering to every thing within the articulation, in the fame manner as the perito- naeum, invefts not only the parietes but all the contents of the abdomen. Phil. Tranf. N° 469. p. 517. The blood-veffels of the cartilages are ib fmall, that they do not admit the red globules of the blood, and confequently they remained unknown till they were difcovered by the modern difcovery of injections, by which the whole vafcu- lar fyftem is filled with a liquid wax, coloured fo as to be diftinguifhed from all other things : nor even by this method are we able to demonftrate the veffels of the true cartilagi- nous fubftance in adult fubjects. But the fat, the glands, and the ligaments will be red with injected vefiels, while not one coloured fpeck appears on the cartilage itfelf. Yet it is evident, that there are veffels there, fince in very young fubjects after a fubtile injection they become fufficiently ob- vious. By this means their courfe is alfo difcovercd, and is found to be as follows.
All round the neck of the bone there 2re a great number of arteries and veins which ramify into fmaller branches, and communicate with one another by frequent anaftomofes like thofe of the mefentery. This might be called the cir- cuits artiadi vafculofus, the vafcular body of the Joint, The fmall branches of the veffels divide into ftill fmaller ones upon the adjoining furface in their progrefs to the center of the cartilage ; and we are very feidom able to trace them into its fubftance, becaufe they terminate abruptly at the edge of the cartilage in the fame manner with the vefiels of the albuginea of the eye, when they arrive at the cornea. The larger vefiels which compofe the vafcular circle plunga in by a great number of holes, and difperfe themfelves into branches between the cartilage and the bone. From thefe again there arifes a crop of ftiort twigs, which fhoot toward the outer furface. Whether thefe ferve for nourishment on- ly to the part, or whether they do not pour forth a dewy moifture of fervice to the functions of the part, it is not eafi- ly determined. It is to be obferved however, that the diftri- bution of the blood-veffels to the articulating cartilages, is very peculiar, and feems calculated for the obviating of great inconveniencies. Had they run to the outer furface, the preflure and motion of the two cartilages muft infallibly have occafioned frequent obstructions and inflammations, which would foon have rendered our motions painful, and at laft have deprived us of them ; but by creeping round the carti- laginous brim where there is little friction, or under the car- tilage where there is none, they are perfectly well defended from thefe accidents. Philof. Tranf. N° 469. p. 518. It would be very happy, if we could trace the nerves of the cartilages ; but in relation to thefe organs we are obliged to be fatisfied with mere conjecture, as to their exiftence here, as well as in many other parts of the body. And tho' from the great infenfibility of cartilages fome perfons have fuppof- ed, that they were furnifhed with no nerves at all, yet when we confider that thefe veffels fcem necefiary to the growth and prefervation of any part, we muft be forced to acknow- ledge their exiftence in this, tho' we can neither fee them nor be fenfible of their effects.
The articulating cartilages are moft happily contrived to all the purpofes of motion in the parts. By their uniform fur- face they move upon one another with cafe ; by their foft- nefs, fmoothnefs and ffipperinefs, their abrafion is prevented, 1 which
