CHAPTER III. 

 MUSCLES AND MOTION. 



Motion and Life. Motion is one of the surest signs of 

 life. While we are sitting still, as we say, there are fre- 

 quent slight motions of the head, body, and limbs. Even 

 during sleep the movements of breathing may be seen; the 

 hand laid upon the chest may feel the beating of the heart, 

 and the finger detect the pulse in a number of places. We 

 must move to get our food, or at least to eat and digest it. 

 We often move to avoid injury. Motion is necessary for 

 speech and in the use of the sense organs. How are all 

 these motions produced? 



Experiments with the Muscles in our own Bodies. I . Clasp the 

 front of the right upper arm ; draw up the forearm strongly and as far 

 as possible. Note the changes that are felt in the biceps muscle. 



Fig. 10. The Shortening and Thickening of the Biceps Muscle in raising the Forearm. 



2. Repeat the experiment, and with the thumb and finger feel the 

 cord, or tendon, at the lower end of the muscle, just within the angle of 

 the elbow. 



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