ELEMENTARY PHYSIOLOGY 



Levers of the third order : 



(i) Raising the forearm. Here the elbow-joint forms the 

 fulcrum, the forearm and hand the weight to be raised, and the 

 power, which is supplied by the contraction of the biceps muscle, 

 is applied at the radius. 



Fig. 71. Raising the Forearm, 



(2) The extension of the leg after bending. The knee-joint 

 is the fulcrum, the lower leg and the foot the weight to be moved. 



Fig. 72. Extension of the Leg. 



and the power is applied at the tibia in front of the leg, by means 

 of muscles passing from it, over the knee-cap, to the hip. 



The student should now endeavour to find for himself other 

 examples of the three orders. To this end he may with advantage 

 consider the motions of the lower jaw, the ribs, and other motions 

 of the limbs. 



