42 HOW THE MUSCLES ARE CONTROLLED. 



of muscle (orbicularis en's, 8, PI. II.) which shuts the mouth, 

 or if more vigorously contracted purses out the lips, as 

 when a child holds up its mouth to be kissed. A similar 

 ring-like muscle (orbicularis palpebrarum, 2, PI. II.) sur- 

 rounds the opening between the eyelids and closes the 

 eyes. 



12. How the Muscles are Controlled. It is very clear 

 that we could not do what we wanted to do if our mus- 

 cles contracted at random: they must be held in control; 

 kept at rest when their action is not needed, and made to 

 work when it is. If the muscles closing the mouth con- 

 tracted when we tried to put food into it we should be 

 in a bad plight. All the muscles are directed and guided 

 in their work by the nervous system (Chap. XVIII.). From 

 the brain and spinal cord nerves run to them, governing 

 all and making them work together in harmony ; those 

 which straighten the elbow-joint are not, for example, 

 permitted to pull when we desire to bend it. In convul- 

 sions the controlling nervous organs cease their guidance; 

 the muscles contract in all sorts of irregular and useless 

 ways; and, often, since those which produce exactly 

 opposite movements contract at the same moment, the 

 whole body is made stiff. 



13. Involuntary Muscles. The muscles hitherto con- 

 sidered are all more or less under the control of our will. 

 We can make them contract or prevent their contraction as 

 we choose. They are called the voluntary muscles. There 

 are other muscles whose working we cannot control; 



12. What power must we have over our muscles ? What is the use 

 of the nerves of the muscles ? In what organs do they commence ? 

 How do the muscles behave during a fit of convulsions? Why? 



13. What are voluntary muscles? Involuntary? Where found? 

 Use? 



