10 MOTION. 



In all these instances, both in the reception of knowledge 

 through any of the senses and of the expression of knowledge 

 through any kind of language, spoken or written, or facial 

 expression, signs, or gestures, some motion is absolutely 

 necessary. 



How are all these motions, so essential to every process of 

 life how are they produced ? 



Experiments with the Muscles in our own Bodies. 



1. Clasp the front of the right upper arm; draw up the 

 forearm strongly and as far as possible. Note what changes 

 are felt in the Biceps muscle. 



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. 



3. Place a weight in the hand, and repeat the act, noting 

 the condition of the muscle during the experiment ; also note 

 the condition of the tendon. 



4. Span the muscle, placing the tips of the fingers in the 

 angle of the elbow, and the tip of the thumb as far as you can 

 up the arm ; again bend the arm. What change in the muscle 

 does this show ? 



5. Any muscle that bends a limb, as does the biceps, is 

 called a Flexor muscle. 



6. Clasp the back of the right upper arm; forcibly 

 straighten the arm. The muscle lying along the back of the 

 arm is the Triceps muscle. It is called an Extensor muscle 

 because it extends, or straightens, the arm. 



7. Clasp the upper side of the right forearm near the el- 

 bow; clench the right hand quickly and forcibly; repeat 

 rapidly. 



8. Notice the thick mass of muscle at the base of the 

 thumb; pinch the forefinger and thumb strongly together. 

 What changes can be seen and felt ? 



