. Human physiology : designed for colleges and the higher classes in schools, and for general reading. ear upon the resistancein a direct line. It is not merely because the back teeth aro THE MUSCLES. 203 Mechanical disadvantage in muscular action. stronger than the front ones, but also because the power is nearerthe resistance, that we can crack a nut more easily with theback, than we can with the front teeth. 301. It is clear that the bictps muscle acts, as it is expressed,at a mechanical disadvantage, if we regard mere power or force,and leave out of view quickness of motion. If it were ins
. Human physiology : designed for colleges and the higher classes in schools, and for general reading. ear upon the resistancein a direct line. It is not merely because the back teeth aro THE MUSCLES. 203 Mechanical disadvantage in muscular action. stronger than the front ones, but also because the power is nearerthe resistance, that we can crack a nut more easily with theback, than we can with the front teeth. 301. It is clear that the bictps muscle acts, as it is expressed,at a mechanical disadvantage, if we regard mere power or force,and leave out of view quickness of motion. If it were insertedfurther down on the forearm, nearer the hand, it could raisemuch greater weights than it now can. And the same can besaid of most of the other muscles of the body. But force issacrificed for the sake of quickness in most cases, because thelatter is more important. In the few cases in which force ismore important, as in the case of the lower jaw just cited, thereverse arrangement is provided. The gain in quickness in thearrangement of the biceps muscle can be illustrated on Fig. 114. FIG. F being the fulcrum, the power in raising the weight, W, to c,if acting at P, passes through the space indicated by the dottedline a. But if it act at p, it will pass through all the space b,and of course raise the weight more slowly than when acting at Most of the muscles work at a mechanical disadvantagein another way. I refer to the direction in which the muscleacts on the bone to be moved. This is seldom at right angles,and therefore a considerable part of the force exerted is can be made clear to you by Fig. 115. Let b representthe bone of the arm, and r its fulcrum, or point of support inthe shoulder. You readily see that if the bone be acted on bya muscle, m, at right-angles to it, it will require less force tomove it to a given point than would be required if the samemuscle were placed in the position represented by n. For the 204 HIMAN PHYSIOLOGY. When !os8
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