of dentine, or ivory, and enamel. The ivory forms the greater
portion of the body and root, while the enamel covers the exposed
surface. The small white cords communicating with the teeth are the
nerves.

The _Tongue_ is a flat oval organ, the base of which is attached to the
os hyoides, while the apex, the most sensitive part of the body, is
free. Its surface is covered with a membrane, which, at the sides and
lower part, is continuous with the lining of the mouth. On the lower
surface of the tongue, this membrane is thin and smooth, but on the
upper side it is covered with numerous papillae, which, in structure,
are similar to the sensitive papillae of the skin.

[Illustration: Fig. 27.
The salivary glands. The largest one, near the ear, is the
parotid gland. The next below it is the submaxillary gland.
The one under the tongue is the sublingual gland.]

The _Salivary Glands_ are six in number, three on each side of the
mouth. Their function is to secrete a fluid called _saliva_, which aids
in mastication. The largest of these glands, the _Parotid_, is situated
in front and below the ear; its structure, like that of all the salivary
glands, is cellular. The _Submaxillary_ gland is circular in form, and
situated midway between the angle of the lower jaw and the middle of the
chin. The _Sublingual_ is a long flattened gland, and, as its name
indicates, is located below the tongue, which when elevated, discloses
the saliva issuing from its porous openings.

The _Pharynx_ is nearly four inches in length, formed of muscular and
membranous cells, and situated between the base of the cranium and the
esophagus, in front of the spinal column. It is narrow at the upper
part, distended in the middle, contracting again at its junction with
the esophagus. The pharynx communicates with the nose, mouth, larynx,
and esophagus.

The _Esophagus_, a cylindrical organ, is a continuation of the pharynx,
and extends through the diaphragm to the stomach. It has three coats:
first, the muscular, consisting of an exterior layer of fibers running
longitudinally, and an interior layer of transverse fibers; second, the
cellular, which is interposed between the muscular and the mucous coat;
third, the mucous membrane, or internal coat, which is continuous with
the mucous lining of the pharynx.

[Illustration: Fig. 28.
A representation of the interior of the stomach.
_1_. The esophagus. _2_. Cardiac orifice opening into
the stomach. _6_.