xv SPECIAL USES OF MUSCLES 211 



ous muscles so that they act correctly without any 

 attention on our part. The muscles of the calf, knee, 

 trunk, back, and neck, and many others, all work to- 

 gether in holding the body erect. 



Sitting differs from standing in that the point of sup- 

 port is changed from the feet to the bones of the pelvis. 

 The muscles of the legs are not active as they are in 

 standing, but the same muscles of the trunk, back, and 

 neck are employed as in- standing. 



The part the nerves play in standing and sitting can 

 be best shown when a person becomes unconscious, as 

 in fainting. He falls to the ground perfectly helpless, 

 although the bones and muscles are not injured in any 

 way. The brain sends no stimuli to the muscles, and 

 they cease to act. The muscles, when in good condi- 

 tion, are the obedient servants of the brain, and respond 

 to the slightest stimulation, but as soon as the brain 

 does not stimulate them they relax, and wait for further 

 orders. 



148. Walking and Running. In standing, both feet 

 rest on the ground all the time ; but in walking, part of 

 the time both feet touch the ground, then the right only 

 while the left swings forward, next the left while the 

 right swings. The foot that is on the ground gives 

 the body a slight push forward which would send it 

 headlong to the ground if it were not checked by 

 placing the other foot forward in time. 



Walking seems to be an act of falling forward and 

 catching one's self. This is accomplished by the use of 

 a large number of muscles. Even the muscles of the 



