| XXX | (181) | XXX |
181 Part I. A N A T O M Y. The external furface is oblique, and irregularly convex, outwards ; the internal pofierior angle of which is fb to be articulated with the cuneiform bone :—The lower prominent, as to have the appearance of a procefs. end is divided into two concave furfaces ; the external The internal fide of this bafe is made plain in the fame is joined with the metacarpal bone of the little finger, way as the external fide of the former bone, while its and the internal one is fitted to the metacarpal bone of external .fide has two hollov/circular furfaces, for joining the third metacarpal bone; and between thefe furthe ring-finger. The ufes of the carpus are, to ferve as a bafe to the faces there is a rougfy fofl'a, for the adhefion of a ligahand, to protect its tendons, and to afford it a free large ment, and lodging mucilaginous glands. The (horter motion. head of the bicornis is inferted into the back-part of this Metacarpus coafifts of four bones, which fuftain the bafe. The two fides of this bone are almofl equally fingers. Each bone is long and round, with its ends flatted ; only the ridge on the fore-part of the body inlarger than its body. The upper end, which fome clines outwards. The tubercles at the fore-part bf call the bafe, is flat and oblong, without any confiderable the root of the head are equal. The motion of this head or cavity ; but it is however fomewhat hollowed, bone is very little more than the firfl: metacarpal one has ; for the articulation with the carpus : It is ‘made flat and and therefore thefe two firmly refill bodies preffed again!! fmooth on the fides where thefe bones ire contiguous to them by the thumb. Or fingers, or both. each other. Their bodies are flatted on their back- Os metacarpi digiti annularis is {horter than the fepart by the tendons of the extenfors of the fingers. cond metacarpal bone.—Its bafe is femicircular and conThe anterior furface of thefe bodies is a little concave, vex, for its conjunbHon with the os unciforme.—On its efpecially in their middle; along which a fliarp ridge internal fide are' two fmooth convexities, and a middle Hands out, which feparates the mufguli interoffei placed foffa, adapted to the lecond metacarpal bone.—The exon each fide of thefe bones, which are there made flat ternal fide has a triangular fmooth concave furface to and plain by thefe mufcles. join it with the fourth one. The anterior ridge of its Their lower ends are raifed into large oblong fmooth body is fituated more to the out than to the in-fide.—*• heads, whofe greateft extent is forwards from the axis The tubercles near the head are equal.—The motion of of the bone.—At the fore-part of each fide of the root this third metacarpal bene is greater than the motion of of each of thefe heads, one or two tubercles Hand but, the fecond. for fixing the ligaments that go from one metacarpal Os metacarpi minimi digiti is the finallefi: and Iharpbone to another, to preferve them from being drawn a- elh—Its bafe is irregularly convex, and rifes flanting funder Round the heads a rough ring may be remark- outwards.—Its internal fide is exadlly adapted to the ed, for the capfular ligaments of the firfl joints of the third metacarpal bone.—The external has no fmooth fingers to be fixed to; and both fides of thefe heads are furface, becaufe it is not contiguous to any other bone; flat, by prefling on each other. but it is prominent where the extenfor carpi ulnaris is The concavity on the fore-part of thefe metacarpal inferted.—As this metacarpal bone is furnilhed with a bones, and the placing their balls on the arched carpus, proper moving mufcle, has the plaineft articulation, is caufe them to form a hollow in the palm of the hand, moft loofely connected and leaft confined, it not only which is ufeful often to us.—The fpaces between them enjoys a much larger motion than any~of the reft, but lodge mufcles, and their fmall motion makes them fit draws the third bone with it, when the palm of the hand fupporters for the fingers to play on. is to be made hollow by its advancement forwards, and Though the offa metacarpi fo far agree, yet they may by the prominence of the thumb oppofite to it. be difHnguifhed from each other by the following marks. The Thumb and four Fingers are each compofed The os metacarpi indicis is generally the longefl.— of three long bones. Its bafe, which is articulated with the os trapezoides, The thumb is fituated obliquely in refpedl of the finis hollow in the middle. ’The fmall ridge on the in- gers, neither oppofite dire&ly to them, nor in the fame ternal fide of this oblong cavity is fmaller than the one plane with them.—All its bones are much thicker and oppofite to it, and is made flat on the fide by the trape- ftronger in proportion to their length, than the bones of zium. The exterior ridge is alfo fmooth, and flat on the fingers are: Which was extremely neceffary, fince its outfide, for its conjunfHon with the os magnum ; im- the thumb counterafts all the fingers. mediately below which, a femicircular fmooth flat furface The firft bone of the thumb has its bafe adapted to {hews the articulation of this to the fecond metacarpal die double pulley of the trapezium.—The edge at the bone.—The back-part of this bafe is flatted, where the fore-part of this bafe is produced farther than any other long head of the extenfor carpi radialis is inferted; and part; and round the back-part of the bafe a rough folia its fore-part is prominent, where the tendon of the flexor may be feen, for the connedlion of the ligaments of this carpi radialis is fixed.—The external fide of the body joint.—The body and head of this bone are of the fame of this bone is more hollowed by the adtion of mufcles, as the offa metacarpi: only that the body is {hort•than the internal.—The tubercle at the internal root of ftiape and the head flatter, with the tubercles at the foreits head is larger than the external.—Its bafe is fo firm- er, part of root larger. ly fixed to the bone it is conneded with, that it has no The itsarticulation of the upper end of this bone is unmotion. common
For it has protuberances and deprefOs metacarpi medii digiti is generally the fecond in fions adapted tothough the pulley of the trapezium ; yet length.—Its Safe is a broad fuperficial cavity, flanting it enjoys a circular double motion, as the joints do where a Vox.. I. No. 8. " 3 Zz round
