INVOLUNTARY MUSCLES. 43 



they are named involuntary muscles. Involuntary muscles 

 are not attached to the skeleton nor concerned in our 

 ordinary movements, but lie in the walls of hollow 

 organs, as the stomach and intestine (Chap. XI.). When 

 they contract they push along the contents of these 

 organs. 



14. As a general rule all the movements most necessary 

 for keeping the body alive, as those which cause the blood 



FIG. 19. The muscular coat of the stomach. 



to flow to all organs or food to travel along the ali- 

 mentary canal, are taken by Nature out of our control, 

 and performed by involuntary muscles. It is, however, 

 impossible to draw a sharp line between voluntary 

 and involuntary muscles. The breathing muscles are 

 partly subject to our will : any one can draw a long 

 breath when he chooses. But in ordinary quiet breath- 

 ing, we are quite unconscious of the working of these 



14. What class of movements is not subject to our will ? Illustrate. 

 What is said concerning the breathing muscles? Give instances in 

 which other voluntary muscles contract against our will. 



