260 MOTION AND COORDINATION 



rule, are attached to the mechanical devices found in the 

 skeleton, and bring about the voluntary movements. The 

 non-striated muscles surround the parts on which they 

 act, and produce involuntary movements. Both, however, 

 are under the control of the nervous system. To bring 

 about the opposing movements of the body, the striated 

 muscles are arranged in pairs ; and to increase their motion, 

 the bones are used as levers. Physical exercise is neces- 

 sary both for the development of the muscles and for the 

 health and vigor of the entire body. 



Exercises. i. Compare the striated and non-striated muscles with 

 reference to structure, location, and method of work. 



2. In what respects is the muscular tissue of the heart like the striated, 

 and in what respects Jike the non-striated, muscular tissue ? 



3. If muscles could push as well as pull, would so many be needed 

 in the body ? Why ? 



4. Locate muscles that work to some extent against elasticity and 

 gravity. 



5. Locate five muscles that act as flexors ; five that act as exten- 

 sors ; two that act as adductors ; and two as abductors. Locate 

 sphincter and radiating muscles. 



6. By what means does the nervous system control the muscles ? 



7. Give proofs of the change of potential into kinetic energy during 

 muscular contraction. 



8. Define the essential properties of muscular tissue and state the 

 purpose served by each. 



9. Describe a lever. For what general purpose are levers used in 

 the body ? What other purpose do they serve outside of the body ? 



10. Why are levers of the second class not adapted to the work of 

 the body ? 



u. Name the class of lever used in bending the elbow ; in straight- 

 ening the elbow ; in raising the knee ; in elevating the toes ; and in 

 biting. Why is one able to bite harder with the back teeth than with 

 the front ones when the same muscles are used in both cases? 



12. Measure the distance from the middle of the palm of the hand 

 to the center of the elbow joint. Find the attachment of the tendon 

 of the biceps muscle to the radius and measure its distance to the 



