[Sidenote: The alimentary canal] The digestive system is the part of our bodies in which the food we eat is so changed that it can be made use of by the little cells in the body. It is composed of a long canal with many parts and enlargements, each part necessary for a certain required work. This canal as a whole is called the _alimentary canal_. [Sidenote: Teeth] The mouth does the first part of the work for the digestive system. Here we find the teeth, which are used for grinding the food. The teeth are composed of three parts, the _head_ (or _crown_), the _neck_ and the _root_. The head, or crown, is very hard. Each tooth is hollow, and in the hollow portion there are nerves and blood vessels. [Sidenote: The salivary glands] Opening into the mouth are three pairs of glands known as _salivary glands_. One pair of glands is located just above the angle of the jaw. It is these glands that become swollen when we have mumps. Another pair of glands is placed just inside the jaw bone, near the root of the tongue, and the third pair is located under the tongue. These three pairs of glands secrete the saliva which moistens the food and aids in digesting the starch. [Illustration: FIG. 82. The alimentary canal.] [Sidenote: The esophagus] The food passes from the mouth; through a passage called the _esophagus_, or gullet, to the _stomach_. [Sidenote: The stomach] The stomach is one of the enlarged parts of the alimentary canal. Its walls are quite thick, and in these walls are thousands of little glands. These glands secrete a fluid called _gastric juice_. When the food enters the stomach it is held there for a long time, and the walls of the stomach squeeze upon it so that the food is mixed with the gastric juice until every bit of it that will be of any use to the body has become fluid in character. Not only does the gastric juice make the food liquid, but it acts on it and changes some of it so that it will be suitable for use by the little cells of the body. As fast as the food is made liquid by the juices of the stomach it is allowed to pass into the intestine through an opening called the _pyloric opening_. [Sidenote: The intestine] The intestine is a long, narrow, twisting and turning tube that is divided into two principal parts, the large and small intestine. In the walls of the intestine are many little glands that secrete a fluid that helps in digesting the food. Two fluids, one made by the liver, the other by the pancreas, are brought into the intestine by two small tubes, which come together in the wall of the intestine six or seven inches below the pyloric opening. These fluids perform a very important part in the digestion of all the different foodstuffs. [Sidenote: Villi and lymphatics]