opening into the larynx. By this means all communication
between the food canal and the air passages is temporarily closed. The
upper muscles of the pharynx now contract upon the food, forcing it
downward and into the esophagus.

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