des. At
the back part are three openings. One, the upper, leads into the nose.
There are two lower openings. One of these leads into the stomach, and
the other leads to the lungs. The back part of the mouth joins the two
tubes which lead from the mouth to the lungs and the stomach, and is
called the _throat_. The mouth contains the _tongue_ and the _teeth_.

[Illustration: THE TEETH.]

~7. The Teeth.~--The first teeth, those which come when we are small
children, are called _temporary_ or _milk teeth_. We lose these teeth
as the jaws get larger and the second or _permanent_ teeth take their
place. There are twenty teeth in the first set, and thirty-two in the
second. Very old persons sometimes have a third set of teeth.

[Illustration: SALIVARY GLANDS.]

~8. The Salivary~ (sal'-i-vary)~ Glands.~--There are three pairs of
_salivary glands_. They form a fluid called the _saliva_ (sa-li'-va). It
is this fluid which moistens the mouth at all times. When we eat or
taste something which we like, the salivary glands make so much saliva
that we sometimes say the mouth waters. One pair of the salivary glands
is at the back part of the lower jaw, in front of the ears. The other
two pairs of glands are placed at the under side of the mouth. The
saliva produced by the salivary glands is sent into the mouth through
little tubes called _ducts_.

~9. The Gullet.~--At the back part of the throat begins a narrow tube,
which passes down to the stomach. This tube is about nine inches long.
It is called the _gullet_, _food-pipe_, or _oesophagus_
(e-soph'-a-gus).

~10. The Stomach.~--At the lower end of the oesophagus the digestive
tube becomes enlarged, and has a shape somewhat like a pear. This is the
_stomach_. In a full-grown person the stomach is sufficiently large to
hold about three pints. At each end of the stomach is a narrow opening
so arranged that it can be opened or tightly closed, as may be
necessary. The upper opening allows the food to pass into the stomach,
the lower one allows it to pass out into the intestines. This opening is
called the _pylorus_ (py-lo'-rus), or gate-keeper, because it closes so
as to keep the food in the stomach until it is ready to pass out.

~11.~ In the membrane which lines the stomach there are many little
pocket-like glands, in which a fluid called the _gastric juice_ is
formed. This fluid is one of the most important of all the fluids formed
in the digestive canal.

[Illustration: GASTR