of our nut, though you may not suspect it. Move your scissors once
more in the same way. Now, you have before you the pattern of the two
jaws on one side of your face, from the ear to the nose; the upper
one, which never moves (as you may convince yourself by placing a
finger on your upper lip when you either speak or eat), and the lower
one which goes up and down. Two pairs of scissors set points to points
give you the whole jaw. The _incisors_ are at the points, they
gallop up and down, and are worthless for doing hard work; the
_molars_ are at the hinges, and move slowly; and if anything tough
has to be dealt with, it comes to them as a matter of course; hence
they are the nutcrackers. You must own that it is pleasant to reflect
thus upon what we are doing every day, and the next time you see a
stonemason moving stones of twenty times his own weight with his iron
bar, ask your papa to explain to you the principle of the lever. After
what I have told you, you will understand it very readily, or at least
enough of it to satisfy your mind.

But, besides this power of moving up and down, the lower jaw possesses
another less obvious one, by means of which it goes from right to left.
This is precisely what naughty children make use of when they grind
their teeth: not that I mean this remark for you, for I have a better
opinion of you than to suppose you do such things. Those who make such
bad use of their jaws deserve to lose the power of ever moving them
thus, and then they would find themselves sadly at a loss how to chew
their bread--for their _molars_ would be of but little service
to them in such a case; as it is chiefly by this second action of the
jaw that the food is pounded. Try to chew a bit of bread by only moving
your jaw up and down, and you will soon tire of the attempt.

One word more to complete my description of the teeth: that portion