318 



ELEMENTARY PHYSIOLOGY 



become a lever of the third order, as when one dances a 

 weight resting upon the toes, up and down, by moving 

 only the foot. In this case, the fulcrum is at the ankle- 

 joint, the weight is at the toes, and the power is furnished 

 by the extensor muscles at the front of the leg (Fig. 6, 1), 



cccps 



fth- 



Fio. 97. — The right Knek-joint. The Outer Half of the Feuttr 

 AND Patella sawn away. 



fein. femur ; pat. patella ; lib. tibia ; ./(6. fibula ; caps, capsule of joint ; 

 I, crucial ligaments ; c, semilunar flbro-cartilages ; e, tendon of extensor 

 muscle. 



which are inserted between the fulcrum and the weight. 

 (Fig. 96, III.) 



11. The Joints of the Body. — It is very important that 

 the levers of the body should not slip, or work unevenly, 

 when their movements are extensive, and to this end they 



