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 i79 Part I. ANA T O M Y. the wrift, a double concave moveable cartilage is interpo- —On the outfide of the ridge there is a broad depreffion* which feems again fubdivided, where the two tendons of fed; which is a continuation of the cartilage that covers the lower end of the radius, and is connedted loofely to the bicornis, or extenfor carpi radialis, are lodged.—The the root of the ftyloid procefs, and to the rough cavity internal fide of this end of the radius is alfo hollowed by the extenfors of the fir ft and fecond joint of the thumb ; there, in which mucilaginous glands are lodged. The ulna is articulated above with the lower end of immediately above which, a little rough furface fhews the os humeri, where thefe bones have depreffions and where the 1'upinator radii longus is inferted.—The ridges protuberances correfppnding to each other, fo as to al- at the fides of the grooves, in which the tendons play, low an eafy and fecure extenfion of the fore-arm to al- have an annular ligament fixed to them, by which the femoft a flreight line with the arm, and fledtion to a very veral (heaths for the tendons are formed.—The fore-part acute angle; but, by the llanting pofition of the pully, of this end of the radius is'alfo deprefled, where the the lower part of the fore-arm is turned outwards in the flexors of the fingers and flexor carpi radialis pafs. extenfion, and inwards in the flection ; and a very fmall The external fide is formed into a femilunated fmooth kind of rotation is likewife allowed in all pofitions, efpe- cavity, lined with a cartilage, for receiving the lower cially when the ligaments are moft relaxed by the fore- end of the ulna.—The loweft part of the radius is formarm being in a middle degree of fledtion. The ulna ed into an oblong cavity ; in the middle of which is a is alfo articulated with the radius and carpus, in a man- fmall tranfverfe rifing, gently hollowed, for lodging mucilaginous glands ; _whiie the rifing itfelf is infinuated inner to be related afterwards. Radius, fo called from its imagined refemblance to a to the conjundion of the two bones of the wrift that are fpoke of a wheel, is the bone placed at the infide of the received into the cavity.—The internal fide of this artifore-arm. Its upper end is formed into a circular little culation is fenced by a remakable procefs of the radius, head, which is hollowed for an articulation with the tu- from which a ligament goes out to the wrift, as the ftybercle at the fide of the pully of the os humeri; and the loid procefs of the ulna with its ligament guards it x>n the half of the round circumference of the head next to the outfide. ulna is fmooth, and covered with a cartilage, in order The ends of both the bones of the fore-arm being to be received into the feinilunated cavity of that bone. thicker than the middle, there is a confiderable diftance Below the head, the radius is much fmaller; there- between the bodies of thefe bones ; in the larger part of fore this part is named its cervix, which is made round which a ftrong tendinous, but thin ligament, is extendby the aftion of the fupinator radii brevis. At the ed, to give a large enough furface for the origin of the external root of this neck, a tuberous procefs rifes ; in- numerous fibres of the mufcles fituated here, that are to the outer part of which the biceps flexor cubiti is in- fo much funk between the bones, as to be proteded from ferted. From this a ridge runs downwards and in- injuries, which they would otherwife be expofed to. wards, where the fupinator radii brevis is inferted; and As the head of the radius receives the tubercle of a little below, and behind this ridge, there is a rough the os humeri, it is not only bended and extended along fcabrous furface, where the pronator radii teres is with the ulna, but may be moved round its axis in any pofixed. fition ; and that this motion round its axis may be fuffiThe body of the radius is not ftreight, but convex on ciently large, the ligament of the articulation is extended its internal and pofterior furfaces; where it is alfo made farther down than ordinary on: the neck of this bone, beround by the equal preffure of the circumjacent mufcles, fore it is connected to it; and it is very thin at its upper particularly of the extenfors of the thumb ; but the fur- and lower part, but makes a firm ring in the middle. faces next to the ulna are flatted and rough, for the ori- This bone is alfo joined to the ulna by a double articugin of the mufcles of the hand ; and both terminate in a lation ; for above, a tubercle of the radius plays in a common fharp fpine, to which the Itrong ligament ex- focket of the ulna ; whilft below, the radius gives the foctended betwixt the two bones of the fore-arm is fixed. ket, and the ulna the tubercle : But then the motion perA little below the beginning of the plain furface, on its formed in thefe two is very different; for, at the upper fore-part, where the flexor rnufcle of the laft joint of end, the radius does no more than turn round its axis the thumb takes its origin, the paflage of the medullary while, at the lower end, it moves in a fort of cycloid veffels is feen flanting upwards. The radius becomes upon the round part of the ulna; and as the hand is artibroader and flatter towards the lower end, efpecialiy on culated and firmly connedled here with the radius, they its fore-part, where its pronator quadratus mufcle is fi- muft move together.—When the palm is turned uppertuated. moft, the radius is faid to perform the fupination; when The lower end of the radius is larger than the fupe- the back of the hand is above, it is faid to be prone. rior ; though not in fuch a difproportion as the upper The Hand comprehends all from the joint of the end of the ulna is larger than its lower end. Its back- wrift to the points of the fingers. Its back-part is conpart has a flat ftrong ridge in the middle, and folfe on vex, for greater firmnefs and ftrength; and it is coneach fide. In a fmall groove immediately on the out- cave before, for containing more furely and convenientfide of the^ ridge, the tendon of the extenfor tertii inter- ly fuch bodies as we take hold of. nodii pollicis plays.—In a large one beyond this, the ten- The hand is. commonly divided into the carpus, medons of the indicator and of the common extenfor rhuf- tacarpus, and fingers. cles of the fingers pafs.—Contiguous to the ulna, there, The Carpus is compofed of eight fmall fpongy is a fmall deprefiion made by the extenfor minimi digiti. bones, fituated at the upper part of the hand, viz. the