40 THE HUMAN BODY. 



are important, force is only a secondary consideration. If 

 we wish to raise the body on the toes, motion is more limited 

 but a great amount of force is necessary. The gastrocnemius 

 and soleus muscles, which form the calf of the leg, are inserted 

 by the tendon of Achilles the largest in the body to the 

 posterior extremity of the calcaneum (or heel-bone), and 

 perpendicular to its axis ; the posterior tibial muscle and the 

 flexors of the toes pass behind the internal malleolus under 

 the calcaneum and under the astragalus, as in the groove of 

 a pulley, and are inserted into the plantar surface of the 

 scaphoid and to the last phalanges of the toes, and these 

 muscles act upon the foot, which serves as a lever of the 

 second order; that is to say, under conditions the most 

 favourable to the power represented by the muscular con- 

 traction. 



