When the bellows are full, we press the handles together and the air is forced out.
~21.~ It is in just this way that we breathe.

When we are about to take a long breath, the muscles pull upon the sides of the chest in such a way as to draw them apart.

At the same time the diaphragm draws itself downward.

By these means, the cavity of the chest is made larger and air rushes in through the nose or mouth to fill the space.

When the muscles stop pulling, the walls of the chest fall back again to their usual position and the diaphragm rises.