212 HUMAN PHYSIOLOGY CHAP. 



arms, which are least concerned, aid somewhat in bal- 

 ancing the body. You will observe that the arm and 

 leg on the same side swing in opposite directions. The 

 fact that so many of the large muscles are employed in 

 walking makes it one of the most beneficial forms of 

 exercise. 



In running, both feet never touch the ground at the 

 same time, but both are in the air for a short period in 

 each leap. The foot, as it leaves the ground, gives the 

 body a much stronger push forward than in walking, 

 and the body is inclined much more. Running is a 

 valuable form of exercise, as it involves so many of 

 the large muscles. One must be careful, however, to 

 breathe properly, and not to continue such severe exer- 

 cise too long. 



In leaping, both feet leave the ground at the same 

 time and are used in throwing the body forward. It is 

 an excellent exercise for the young. Swimming is a 

 mode of moving the body along in the water by the 

 combined action of the muscles of the arms and legs. 

 No form of exercise brings into use a larger number of 

 muscles, or is better to give us general bodily strength 

 than swimming. 



149. Muscles of Expression. Muscles of the face 

 and other parts of the body are used to indicate feel- 

 ings of pleasure, pain, sorrow, confidence, anger, fear, 

 etc. The facial muscles are all flat, and attached to the 

 skin in such a way as to cause the mouth and eyes to 

 take a great variety of positions when they contract. 



The muscles of expression may be trained by a little 



