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Part II. i98 A N A T O M Y. examine carefully the fituation of this mufcle, we will the other in the broad concave fide of the lower extreof the radius. find it more difpofed to maintain thefe bones in that po- mityIt has or tendinous frasnum belonging to fture, by co-operating with the brachialis, than to-ex- it, one enda ligamentary of which is fixed in the interofleous ligament, tend them by affifting the other anconsei. the other in the inner edge of the bafis of the radius. Sect. VI. Muscles which move the Radius upon the Ulna. SUPINATOR LONGUS five MAJOR. This is a long flat mufcle, lying on the external condyle of the os humeri, and on the convex fide of the radius from one end to the other. It is fixed by flefliy fibres to the external inter-mufcular ligament, and to the crifta of the external condyle of the. os humeri, for five or fix fingers breadth above the condyle, between the brachkeus and anconaeus externus. From thence it runs along the whole convex fide of the radius, and is inferted by a flat narrow tendon, a little above the ftyloid apophyfis in the angle between the concave and flat fnjes of the extremity of this bone. SUPINATOR BREVIS five MINOR. This is a fmall thin flefliy mufcle, furrounding'a great portion of the upper third part of the radius. It is fixed by one end to the lower part of the external condyle of the os humeri, to the external lateral ligament of the joint, to the annular ligament of the radius, and to, part of the lateral eminence in the head of the ulna. From thence it paflfes obliquely over the head of the radius, covering fome part of it; and running down upon, and in fome meafure furrounding the neck, it turns in under the bicipital tuberofity, and is inferted by the fide of the interoffeous ligament in the infide of the fuperior quarter of the bone, and even a little lower. PRONATOR TERES five OBLIQUUS. This is a fmall mufcle, broader than it is thick, fituated on the upper part of the ulna oppofite to the fupinatbr brevis. It is fixed to the internal condyle of the os humeri, partly by fleftiy fibres, and partly by a tendon common to it with the ulharis intefnus. From thence it pafles obliquely before the extremity of the tendon of the brachisus, and reaches to the middle part of the convex fide of the'radius, where it becomes flat, and is inferted below the fupinator brevis by an extremity almoll wholly flelhy. Pronator Quadratus fve Transversus. This is a fmall flefliy mufcle nearly as broad as it is long, lying tranfverfely on the infide of the lower extremity of the fore-arm. It is fixed by one fide or edge in the long eminence at the lower part of the internal angle of the ulna, and by
The Uses of the Mufcles •which move the Radius on the Ulna. The fupinator longus allifts in the motion of fupination, and is alfo a flexor of the fore-arm. The fupinator brevis feems to have no other ufe than what is exprefled by its name; and as it is a Ihort fmall mufcle, it muft be very weak. The pronator teres can have no other action but that of pronation, in the different fituations of the radius, whether that bone be in a middle ftate between pronation, and fupination, or in the greateft degree of fupination ; and, in this cafe, though it is but a fmall weak mufcle, it overcomes the fupinator longus. The pronator quadratus is capable of no other motion but pronation, and it adfs with much more force than its congener the pronator teres. Sect. VII. The Muscles which move the Carpus upon the Fore-arm. U LN ARI S. This is a long mufcle, fleftiy at its upper extremity, and tendinous at the other, fi mated on the outer part of the ulna. It is fixed by its upper part in the backfide of the long or internal condyle of the os humeri, in that part of the olecranum which is next the condyle, along the upper half ofjjthe ulna very nearly; and to the middle common tendon of the neighbouring mufcle, termed commonly profundus. It runs in the dire&ion of the external angle of the ulna, and ends by a long tendon, in the os pififorme or orbiculare of the carpus, reaching likev/ife to the os uaciforme, being united to the ligament common to thefe two bones. RADIALIS INTERNUS. This is a long mufcle very like the foregoing, but fituated more obliquely. Its flefliy portion is fixed, by a ftiort tendon, to the outer and upper fide of the inner condyle of the os humeri. From thence it pafles obliquely toward the radius ; and running along about two thirds of that bone, it forms a long tendon, which pafles under a particular annular ligament, and under the infertion of the mufculus thenar. This tendon is at length inferted chiefly in the infide of the bafis of the firft metacarpal bone, and often in the fecond likewife, and a little in the firft phalanx of the thumb,, having firft pafled through the channel of the os trapezium, which fuftains the thumb. ULNAR IS.
