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and thefc are very firm and folid : the fhort ones arc not of half the length of thefe, and are not indeed regularly of the fame length one with another, and differ accordingly in fine- nefs, the long being fomewhat harfh, the fhort perfectly foft and fine, and no other than a moft fmooth down. Thefe are what make the fur ufed by the hatters; and this diverfity of hair on the animal is no way fingular, feveral creatures having the fame ; a long hair for a fort of ornament, and a downy fur for warmth and for defence. The tail lias no hairs, but is black and fcaly, fomewhat in the manner of the skin of fifties; the fcales are as thin as parch- ment, and are joined to and by a firm cuticle; the tail is ten or eleven inches long, and four or five broad, fmall at its in- fertion, then fwelling out toward the middle, and becoming a- gain a little fmaller juft at the extremity, fo that it is of a fort of oval figure. The anus and paflage for the urine are contained in one common aperture ; the penis in the male lies in the upper part ot this aperture, and is boney, and under this aperture is by means of a membrane divided into two parts, each of which terminates in a lateral finus. For the ftruclure of the bags which contain thecaftor. See Castor. We have not the beaver now wild with us in England, but there is great room to believe, that it once was fo, from what our own authors have ("aid of it. FIBRARLE, in natural hiftory, the name of a clafs of foffil bodies, the greateft part of which have been very improperly called by the writers of foffils, fibrofe talcs, they being ot a very different fubftance and ftruclure of parts from the talcs,, • and having none of their diftinguifhing characters. The word is derived from the latin fibra, a fibre, or filament, thefe bodies being all compofed of arrangements of parallel fila- ments or fibres. See Tab. of Foflils, Clafs I. The Fibrarite in general are folTils compofed of parallel filaments ufually remaining fodiftinit as to prefcrve in the whole mafle; a thread like texture ; but fometimes uniting fo as to form plates or flakes, refembling thole of the talcs in external fi- gure. They are bright, and in fome degree tranfparent ; not giving fire with fteel, nor fermenting with, or foluble in acid menftrua. Hilh Hift. of Foff. p. 88.
Of this clafe of bodies there are two diftincl: orders, and under thofe four genera. The firft order is of tnofe which are com- pofed of filaments ranged perpendicularly in the tnafs, not flex ile nor elaflic, and readily calcining in the fire. Thefe are the bodies which have been called the fibrofe talcs. The fecond order is of thofe which are compofed of filaments ranged horrizontally in the mafTes, and are flexile and elaftic in fome degree, and not calcining in the fire. The firft genus of the firft order, is of thofe fibrofe bodies which are not ela- ftic, and are compofed of ftrait and continuous filaments call cd tricheriae. The fecond is of thofe which are not elaftic, and are compofed of fhort and abrupt filaments, the lachni des. The firft genus of the fecond order is of thofe fibrofe bo- dies which are flexile and elaftic, and are compofed of ftrait and continous filaments, as the asbefti. The fecond is of thofe fibrofe bodies which are flexile and elaftic, and are compoled of fiiort and abrupt filaments, the amianthi. FIBROSE roots-, thofe which confift wholly of fmall fibres, fuch as the roots of the meadow-grafs, pinks, and feveral other flowers. When z fibrofe root penetrates ftrait into the ground, it is called perpendicular ; when it creeps under the lurface, horizontal; when fomewhat thick, it is called fiejhy ; when very thin, capillary ; when it runs all the way undivided, fun- fle\ when divided, or when it fends off fmaller roots, branch- ed\ when its furface is covered with extremely fhort and fine fibres, hairy. See Root. FIBULA, in natural hiftory, a name given to a clafs of the echinodermata, which have their mouth in the middle of the bafe, and the aperture of the anus on one edge. Thefe are found principally among the foffil kinds, and feem to have had their fliells of the affiliated kind, or compofed of fmall plates joined tranfverfely to one another. Of this clafs, there are two genera, the conulus and difcoides. Kleine's Echi- nod. See Conulus and Discoides. Fibula, in anatomy [CycL) — The upper extremity of this ■ bone is a kind of tuberofity or head, obliquely flatted by a fmall cartilaginous plane, by which it is articulated with the cartilaginous furface, at the lower part of the external condyle of the tibia. It terminates backward by a kind of fhort blunt . point directed upward. The lower extremity is broader, flat- ter, and more oblong than the upper ; it is partly a continua- tion of the body of the bones, and partly an epiphyfis in children ; the marks of which are quite loft in a more advan- ced age. It has in a manner three fides, one rounded like a tuberofity, one flat, and the third narrow ; when it is placed in the lateral cavity of the bafis of the tibia, it makes the outer ankle oppofite to the inner ankle. In its natural lituation, it reaches much lower down than the bafis of the tibia, and ends in a point turned a little backward. The flat fide is cartilaginous, and turned toward the cartilagi- nous fide of the inner ankle, with which, and with the in- ferior fide of the bafis of the tibia, it completely forms the cavity by which the leg is articulated with the foot. The
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narrow fide is turned backward, and near its lower oart I fmall, oblong, unequal feffijh, formerly believed to be for 'tV paflage of a tendon, in which a fmall mucilaginous »hnj i! lodg'd The point by which the bafis of fiRg^ a (mall fmooth furface immediately below the narro Yd for the infertion of an annular ligament. W '
The body of this bone is long and fmall, more or left contort ed, and irregularly triangular. Near the two extremities it contraas into a kind ot neck, and a little below the middle it is often bent inward ; but this curvature feems chiefly owing to the method of dreffing children, for we fometimes meet with the bone very ftrait. It is diftinguiihed in an irregular manner into three fides, and three 'angles, principally towards its lower part. The outfide is the moft confiderable: the up- per part of it is more or lefs hollowed ; afterwards it grows round, and altering its direflion, becomes almoft pofterior in the lower halt. The pofterior fide is more or lefs convex to- ward the upper part, thence it grows flat, and turning in the fame manner as the former, it becomes nearly internal to- ward the lower part. The inner fide has likewife a turn near its middle, and becomes anterior from thence downward ; and this turn is marked by an oblique line, which runs down on rhis fide, from behind, forwards, and divides it into two. Thefe fides ferve partly for mufcles to lie upon, and partly for their infertions. The internal angle of the fibula anfwers to the external pofterior angle of the tibia, and both ferve for the infertion of the interoffeous ligament of the leg ; the other two angles are more or lefs acute, efpecially the anterior, which is fometimes like a kind of crifta, and terminates be- low in a fmall triangular furface.
The internal ftruclure of the fibula, though a very fmall bone, is like that of the other long bones ; it is articulated by its upper extremity, with the inferior furface of the external condyle of the tibia ; this articulation is an arthrodia, with a very fmall degree of motion. The inferior extremity is arti- culated by its cartilaginous fide, partly with the lateral depref- fion in the bafis of the tibia, and partly with the fiift bone of the foot, completing the ginglymus between the leg and that bone. Wir.Jlovti, Anatomy, p. 95.
Cartilage! of the Fibula. The fibula has two cartilages, one lying on the upper extremity of that bone, for its articulation with the fmall cartilaginous furface in the head of the tibia ; the other cartilage covers the infide of the inferior extremity! or the outer ankle, near the point of which pofteriorly, there is a fuperficial cartilaginous incruftation for the paflage of the tendons of the mufculi peronsi. The cartilage at the upper extremity ferns thicker, than that at the lower. IPmflmi'i Anatomy, p. 128.
Ligaments 'oft!:' Fibula. This bone is joined to the tibia by nine ligaments, four at each end, and one in the middle, called the interofleous ligament. The four at the upper extremity are fhort, very ftrong, more or lefs oblique and compound ; two of them are anterior and two pofterior, and they lie on each other | the fuperior ligaments furrounding the articulation more clofely then the inferior, which have a fmall void fpace, and are weaker than the former ; they are all faftned to the cap- fular ligament, which runs in between them and the articula- tion, and they are infertcd round the edges of the cartilaginous furfaces in each bone.
The ligaments of the lower extremity of the fibula which runs below the tibia, and forms the outer ankle, are much ftronger, thicker, more complex, broader, longer, and more oblique, than thofe of the fuperior extremity ; and are like thofe difpofed, two before, and two behind. They are fixed to the anterior and pofterior edge of the lateral depreffion at the inferior extremity of the tibia, and from thence they run down on the lower end of the fibula.
The two inferior ligaments are longeft, and they are fixed anteriorly and pofteriorly at the lower end of the outer ankle; the two fuperior are fixed more clofely, and nearer each other', but there is ftill a fmall fpace between them, which is filled with fat. As the two bones touch each other only by the up- per part of the cartilaginous furface of the outer ankle, and the fmall cartilaginous border in the lower edge of the depref- fion of the tibia, the middle fpace between them is filled by a capfular ligament, which lines each fide of the bones, and is continued down to the true articulation of the external an- kle, with the inferior edge of the bafis of the tibia. The middle or interofleous ligament of the two bones of the leg, fo called becaufe it fills up all the fpace left between them, being ftretched from one to the other, is fixed along the pof- terior external angle of the tibia, and the neighbouring angle of the fibula. It is made up chiefly of two planes of very oblique ligamentary fibres, which croft each other, and at dif- ferent intervals feem to be multiplied. It is perforated both above and below, and fometimes in feveral places befide, for the paflage of the blood-veflels and nerves. It is not a liga- ment intended for the tying thefe two bones together, but is rather a ligamentary feptum for the infertion of mufcles, Ap- plying in this refpeft the place of a bone, and feeming indeed to be partly a continuation of the periofteum of the tibia and fibula. At the lower part of each ankle, there are common-
