WALKING 



man's erect posture. In most animals, the four limbs 

 are adapted chiefly to locomotion, so that their heads and 

 mouths have to do much of the work which we do with 

 our hands. 



Locomotion. Locomotion for man presents more dif- 

 ficulties than for four-footed animals, since the support 

 afforded by the ground is limited to his two feet in- 

 stead of to their widely separated four. As a result, 



FIG. 48. Analysis of a single step in bent-knee walking. (Bradford.) 



the difficulty of maintaining his balance is what makes 

 a baby so slow in learning to stand and walk. In walk- 

 ing, the weight is alternately supported by first one 

 leg and then the other. The leg which supports the 

 weight is ordinarily straightened to its full length. At 



