. Human physiology. the Fig. 62.—A Lever ofSecond Order. P, power ; w, weight; F, fulcrum. Fig. 63.—A Crowbar, used as a Lever of theSecond Order. The see-saw. (3; The beam of a pair of scales. (4) The poker, whenresting on a bar of thegrate, and used to lift thecoals in the fire. Levers of the secondorder are those in whichthe weight is between thefulcrum and the following are ex-amples :— (1) The crowbar,when used for lifting aweight, while one of its 0. Fig. 64.—A Lever of theThird Order. -The Treadle, illustrating a Leverof the Third Order. Fig. w, weight; p, power ; f, fulc
. Human physiology. the Fig. 62.—A Lever ofSecond Order. P, power ; w, weight; F, fulcrum. Fig. 63.—A Crowbar, used as a Lever of theSecond Order. The see-saw. (3; The beam of a pair of scales. (4) The poker, whenresting on a bar of thegrate, and used to lift thecoals in the fire. Levers of the secondorder are those in whichthe weight is between thefulcrum and the following are ex-amples :— (1) The crowbar,when used for lifting aweight, while one of its 0. Fig. 64.—A Lever of theThird Order. -The Treadle, illustrating a Leverof the Third Order. Fig. w, weight; p, power ; f, fulcrum. ends rests on the ground. (Fig. 63.) (2) The wheelbarrow. In this case the fulcrum is the pointwhere the wheel rests on the ground. Levers of the third order are those in which the power is 56 ELEMENTARY PHYSIOLOGY applied at a point between the fulcrum and the weight. As an ex-ample we may mention— The treadle of a machine. We may now proceed to notice examples of levers which areto be found in the human skeleton. Levers of the first order :— (i) The head rocking on the atlas. The fulcrum is formedby those parts of the atlas that support the condyles of theoccipital bone (see page 19). When the muscles of the back ofthe neck contract, the face is raised. When the antagonistic
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