. The physiology of the domestic animals; a text-book for veterinary and medical students and practitioners. Physiology, Comparative; Domestic animals. Fig. -Complete Contraction of Biceps. (Perrier.) Fig. 290.—Motion op Head as illustra- ting Action op Lever of First Class. (Biclard.) a, fulcrum of the lever, cb; a b is the weight-arm, for the head tends to fall forward by its own weight acting in the line, r. This is prevented by the contraction of the muscles of the back of the neck acting on the power-arm, c a, in the line, P. power is lost in velocity, and vice versa. Thus, in the c
. The physiology of the domestic animals; a text-book for veterinary and medical students and practitioners. Physiology, Comparative; Domestic animals. Fig. -Complete Contraction of Biceps. (Perrier.) Fig. 290.—Motion op Head as illustra- ting Action op Lever of First Class. (Biclard.) a, fulcrum of the lever, cb; a b is the weight-arm, for the head tends to fall forward by its own weight acting in the line, r. This is prevented by the contraction of the muscles of the back of the neck acting on the power-arm, c a, in the line, P. power is lost in velocity, and vice versa. Thus, in the case of the third class of lever, power is exchanged for velocity. This may be well represented in the movement of flexion of the human forearm (Figs. 288 and 289). The fulcrum is there found in the elbow-joint, the power is the insertion of the biceps muscles in the bone of the forearm in front of : , i | the joint, the weight is carried by the hand. In this arrange- '.,....i ment it is evident that slight motion at the insertion of the biceps will be greatly multiplied in the case of the hand. Thus, say that the distance from the elbow-joint to the tip of the hand is eighteen inches, the dis- tance from the elbow-joint to the point of insertion of the biceps one inch, motion of one inch at the inser- tion of the biceps will produce motion at the hand of an arc of a circle whose cord is eighteen inches. The forearm is, therefore, in this action an example of the third class of lever. In general, in the animal body, the point of application of the power .developed by muscular contraction lies near the fulcrum: hence the conditions favor the production of velocity of movement at the expense of power, tor the power-arm is always shorter than the weight-arm. ., .. ^e conditions are, however, reversed in the case of the extensor muscles of tne limbs when in contact with the ground. Here the joint nearest to which the muscle is inserted is the point of application of the
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectphysiol, bookyear1890
