6.  The Mouth.—­The space between the upper and the lower jaw is called the mouth.  The lips form the front part and the cheeks the sides.  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:  GASTRIC GLAND.]

12.  The Intestine(in-tes’-tine).—­At the lower end of the stomach the digestive canal becomes narrow again.  This narrow portion, called the intestine, is about twenty-five feet long in a grown person.  The last few feet of the intestine is larger than the rest, and is called the colon.  This long tube is coiled up and snugly packed away in the cavity of the abdomen.  In the membrane lining the intestines are to be found little glands, which make a fluid called intestinal juice.