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 M Y Part II. I5>S A N A T It is fixed ’m the pofterior half of the'infra-fpinal ca- rate it from the ribs, not only dire&ly, but likwife obvity or foiTa, and to the correfpOnding part of the bafis liqtiely in many different ways. The arm being lifted directly upward, the lateral, anterior, and pofterior porof the fcapula. From-thence arife a great number of (hort fleihy fibres, tions of this mufcle may bring the arm, fo raifed, for7 which run more or lefs obliciuely, and end in a middle ward and backward. tendinous plane, which terminates a little below the The latiffimus dorfi ferves in general to bring down the arm when raifed; it alfo ferves to deprefs the ftoulbroadeft part of the fpine of the fcapula, under tire root der, or to maintain it in that fituation againft any force of the acromium. Then the hefty fibres, leaving the bone, unite in that endeavours to raife it; as when we lean upon the one flefty mafs, which, palling under the acromium, o- elbow in fitting, or walk upon crutches. ver the articulation of the head of the os humeri, and The peAoralis major ferves in general to bring the adhering to the capfular ligament, terminates there in a arm near the ribs, to prefs it ftrongly againft them, and flat broad tendon, which, adhering likewife to the capfula, to carry it towards the fore-part of the thorax. is afterwards inferred in the greater middle furface of the The teres major, by being inferted in the os humeri in a direction parallel to the latiffnnus dorfi, becomes a great tuberofity of the head of the os humeri. congener to the fuperior and pofterior portion of that mufcle; and accordingly moves the os humeri in the SUPRA-SPINATUS. fame manner with it. It turns the bone round its axis, This is a thiSk narrow mufcle, in fome meafure pen- when the fore-arm is carried behind the back. niform, filling all the fupra-fpinal cavity of the fcapula. It likewife pulls the arm diredtly backward, without It is fixed to all the pofterior half of the fupra-fpinal moving it round its axis. fofl’a; and fometimes its infertion reaches near the neck The coraco-brachialis brings the arm to the forefide of the bone. There the fibres leave the furface of the of the thorax, raifing it at the fame time ; and, in this bone, and pafs between the acromium and neck of the cafe, it may be reckoned a congener or affiftant to the pecfcapula, under the arch formed by the acromium and ex- toralis major in great efforts; and may perform the fame tremity of the clavicle, and under the ligament between motion by itfelf, when no great force is neceflary; as the acrorriium and apophyfis coracoides ; being afterwards when the whole arm hangs down, and is moved backinferted in the fuperior furface of the great tuberofity of ward and forward like a pendulum, the motion forward the head of the os humeri, very near the bony channel, being performed by the coraco-brachialis, and the motion backward by the teres major, its antagonift. This mcfcle may likewife move the fcapula on the os C O RAC O-B R A C H I ALI S. humeri firmly depreffed, as when fitting in a chair This is a long mufcle lying on the infide of the up- we takekept fall: hold of the edge of it with the hand. In per half of the os humeri. this cafe the coraco-brachialis may bring die arcromium It is fixed above to the point of the coracoid apophyand the inferior angle of the fcapula, near fis, between the infertions of the biceps and pedtoralis downward, the vertebra:. It ferves likewife to bring the arm to its minor, by a tendon, which, as it defcends, adheres for fituation, after it has been turned by the latifiia good way to the tendons of thefe two mufcles. Af- former mus dorfi, in order to apply the hand to the back ; and terwards it becomes flefty, and is inferted by a broad then it turns the os humeri its axis in a contrary.dithin extremity, with a final! mixture of tendinous fibres, re&ion to that given it by theuponother mufcle. in the middle part of the os humeri. The fupra-fpinatus joins with the deltoides in lifting up the arm; this mufcle beginning that aftion, and the SUBSCAPULARIS. deltoides continuing it. The infra-fpinatus being inferted by its tendon in the This mufcle is of the fame breadth and length with middle furface of the great tuberofity of the os humerij the fcapula, of which it occupies all the inner or con- muft perform different motions according to the different cave fide; and from this fituation it has its name. It is fituations of that If it affs while the arm hangs thick, and. made up of feveral penniform portions nearly down, parallel to bone. the trunk of the body, it may move in the fame manner with the deltoides. the os humeri round its axis, from before outward; and It is fixed in the internal labium of the whole bafis, if the fore-arm be at the fame time bent, and in almoft the whole internal furface of the fcapula; confequently, turn the hand from the body, its flefty portions lying in the intervals between the bony it will the arm hangs down in its natural fituation, lines, when thefe are found. Near the neck, they leave theWhen may turn it round its axis, from withthe bone, and form a very broad tendon which is infert- out fubfcapularis forward, when in this fituation we beat ed in the furface of the fmall tuberofity of the head of the breaft v/ithastheit happens fore-arm bent; and it likewife ftrongthe os humeri. ly aflifts the Jatifiimus doifi, when we turn the hand bethe back. Uses of /^/Muscles which move the Os Humeri hindWhen the arm being raifed, we move it backward, as on the Scap-ula. in giving a back-ftroke with the elbow or fift, the fubThe deltoides, from the difpofition of its infertions fcapularis hinders, the head of the os humeri from being in the fcapula and clavicle, may raife the arm, or fepa- luxated forward. The