THE BTCEPS-MUSCLE. 4! 



of the middle finger to show the ending of tendons 

 on it. 



10. How we may Recognize the Working of a Muscle. 

 The shortening of a muscle, when it is at work, is suf- 

 ficiently shown by the way it pulls the bones; as when 

 we bend the elbow-joint or the fingers. The thickening 

 may be seen and felt on the biceps-muscle (Fig. 18), in 

 front of the humerus, when the elbow is bent; or on the 

 muscles of the ball of the thumb, when we move the 



FIG. 18. The biceps-muscle and the arm-bones, to illustrate how the elbow-joint 

 is bent, when the biceps-muscle contracts and becomes shorter and thicker. 



thumb so as to make it touch the little finger. When a 

 muscle contracts, its belly becomes harder. The swell- 

 ing and hardening of a contracted muscle are daily illus- 

 trated when a school-boy bends his elbow as powerfully 

 as he can and then invites another to feel his " biceps." 

 11. Muscles not directly attached to the Skeleton. Most 

 of these surround openings, which they close when they 

 contract. Thus around the mouth-aperture is a ring 



10. How may we recognize the shortening of a working muscle ? 

 The thickening ? The hardening ? 



11. Give examples of muscles not directly attached to bones. 



