3. In the esophagus the food is forced along by the successive contractions of muscles, starting at the upper end of the tube, until the stomach is reached. Swallowing is doubtless aided to some extent by the force of gravity. That it is independent of this force, however, is shown by the fact that one may swallow with the esophagus in a horizontal position, as in lying down. [Fig. 68] Fig. 68—*Gastric Glands.* _A._ Single gland showing the two kinds of secreting cells and the duct where the gland opens on to the surface. _B._ Inner surface of stomach magnified. The small pits are the openings from the glands. *The Stomach.*—The stomach is the largest dilatation of the alimentary canal. It is situated in the abdominal cavity, immediately below the diaphragm, with the larger portion toward the left side. Its connection with the esophagus is known as the _cardiac orifice_ and its opening into the small intestine is called the _pyloric orifice_. It varies greatly in size in different individuals, being on the average from ten to twelve inches at its greatest length, from four to five inches at its greatest width, and holding from three to five pints. It has the coats common to the canal, but these are modified somewhat to adapt them to its work. _The mucous membrane_ of the stomach is thick and highly developed. It contains great numbers of minute tube-shaped bodies, known as the _gastric glands_ (Fig. 68). These are of two general kinds and secrete large quantities of a liquid called the gastric juice. When the stomach is empty, the mucous membrane is thrown into folds which run lengthwise over the inner surface. These disappear, however, when the walls of the stomach are distended with food. _The muscular coat_ consists of _three_ separate layers which are named, from the direction of the fibers, the circular layer, the longitudinal layer, and the oblique layer (Fig. 69). The circular layer becomes quite thick at the pyloric orifice, forming a distinct band which serves as a valve. [Fig. 69] Fig. 69—*Muscles of the stomach* (from Morris’ _Human Anatomy_). The layer of Longitudinal fibers removed. The outer coat of the stomach, called the _serous coat_, is a continuation of the peritoneum, the membrane lining the abdominal cavity. *Stomach Digestion.*—In the stomach begins the definite work of dissolving those foods which are insoluble in water. This, as already stated, is a double process. There is first a chemical action in which the insoluble are changed into soluble substances, and this is followed immediately by the dissolving action of water. The chief substances digested in the stomach are the proteids. These, in dissolving, are changed into two soluble substances, known as _peptones_ and _proteoses_. The digestion of the proteids is, of course, due to the