8 PHYSIOLOGY. 



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

 dition 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 ? Any 

 muscle that bends a limb, as does the biceps, is called a flexor muscle. 



5. 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. 



6. Clasp the upper side of the right forearm near the elbow ; 

 clench the right hand quickly and forcibly ; repeat rapidly. 



7. 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 ? 



8. Place the hand on the outside of the shoulder ; raise the arm to 

 a horizontal position; repeat with a weight in the hand. 



Fig. 2. The Shortening and Thickening of the Biceps Muscle in raising the 

 Forearm. 



9. Stand erect with the heels close to each other, but not quite 

 touching; let the arms hang freely by the sides; rise on tiptoes, 

 without moving otherwise ; repeat ten times. 



10. Place the tips of the fingers on the angles of the lower jaw; 

 shut the teeth firmly on a piece of rubber, and note the bulging of the 

 masseter muscles. 



