. Human physiology (Volume 1) . Action of the , the Scapula ; B, the Os humeri; C, the Deltoid. Figure 88, strikingly exhibits the disadvantages of the deltoid,so far as regards the place of its insertion into the lever ; but manymuscles have insertions much less favourable than the biceps, D, for example, in Fig. 89, — the muscle which bendsthe forearm on the arm, — is attached to the forearm ten timesnearer the elbow-joint, or the fulcrum, than to the extremity ofthe lever; and if we apply the argument to it, — supposing theweight of the globe, in the palm of the hand, t
. Human physiology (Volume 1) . Action of the , the Scapula ; B, the Os humeri; C, the Deltoid. Figure 88, strikingly exhibits the disadvantages of the deltoid,so far as regards the place of its insertion into the lever ; but manymuscles have insertions much less favourable than the biceps, D, for example, in Fig. 89, — the muscle which bendsthe forearm on the arm, — is attached to the forearm ten timesnearer the elbow-joint, or the fulcrum, than to the extremity ofthe lever; and if we apply the argument to it, — supposing theweight of the globe, in the palm of the hand, to be fifty-fivepounds and the weight of the limb five pounds, — it would haveto act with a force equal to sixty times ten, or six hundred pounds,to raise the weight. Muscles, again, are attached to the bones at unfavourable they were inserted at right angles in the direction of P P, , the whole power would be effectually applied in moving the Fig. Action of the Biceps. A, the Os humeri; B, the Ulna; C, the Radius; D, the Biceps; E, insertion of the Biceps into the Radius. limb. On the other hand, if the muscle were parallel to the bone,the resistance, it is obvious, would be infinite, and no effect couldresult. In the animal, it rarely happens that the muscle is inserted APPLICATION OF MECHANICAL PRINCIPLES. 387 at the most favourable angle : it is generally much smaller than aright angle. Reverting to the deltoid, this muscle is inserted intothe humerus at an angle of about ten degrees. Now, a poweracting obliquely upon a lever, is to one acting perpendicularly, asthe sine of inclination, represented by the dotted line F s, Fig. 86,to the whole sine P P. In the case of the deltoid the proportionis as 1,736,482 to 10,000,000. Wherefore, if the muscle had tocontract with a force of one hundred and eighty pounds, owing tothe disadvantage of its insertion near the fulcrum, it would have,from the two causes combined, to exert a for
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Keywords: ., bookcentury1800, bookdecade1840, booksubjectphysiology, bookyear1
