_tendons_. If you will place the thumb of your left hand upon the wrist
of the right hand, and then work the fingers of the right hand, you may
feel these cords moving underneath the skin.

~7. What the Muscles Do.~--With the left hand grasp the right arm just
in front of the elbow. Now shut the right hand tightly. Now open it.
Repeat several times. The left hand feels something moving in the flesh.
The motion is caused by the working of the muscles, which shorten and
harden when they act.

~8.~ All the movements of the body are made by means of muscles. When we
move our hands, even when we close the mouth or the eyes, or make a wry
face, we use the muscles. We could not speak, laugh, sing, or breathe
without muscles.

~9. Self-acting Muscles.~--Did you ever have a fit of sneezing or
hiccoughing? If you ever did, very likely you tried hard to stop but
could not. Do you know why one cannot always stop sneezing or
hiccoughing when he desires to do so? It is because there are certain
muscles in the body which do not act simply when we wish them to act,
but when it is necessary that they should. The muscles which act when we
sneeze or hiccough are of this kind. The arm and the hand do not act
unless we wish them to do so. Suppose it were the same with the heart.
We should have to stay awake all the while to keep it going, because it
would not act when we were asleep. The same is true of our breathing. We
breathe when we are asleep as well as when we are awake, because the
breathing muscles work even when we do not think about them.

~10.~ The stomach, the intestines, the blood-vessels, and many other
organs within the body have this kind of muscles. The work of these