, as the lion, have the cuspids, or
canine teeth, largely developed, and the molars have sharp cutting
points. Those animals that feed on grass and grain, as the horse and
the sheep, have their molar teeth more rounded and flat on the crown.
The human teeth are adapted to feed on fruits, grain, or flesh, as
they are less pointed than those of the cat, and more pointed than
those of the sheep.

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216. Give the names of the permanent teeth. What teeth have but one
root, or "fang"? How many roots have the molars of the upper jaw? Of
the lower jaw? What is said of the shape of the teeth in different
species of animals?

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217. The teeth are composed principally of two substances--the
_i'vo-ry_ and the _en-am'el_. The internal part of the tooth or the
ivory, is harder and more enduring than bone, and forms the body of
the tooth. The enamel is remarkable for its hardness, and varies
somewhat in color with the age, temperament, habits, and manner of
living of different individuals. When any part of the enamel is
destroyed, it is never regenerated.

[Illustration: Fig. 56. A side view of the body and enamel of a front
tooth.]

[Illustration: Fig. 57. A side view of a molar tooth. 1, The enamel. 2,
The body of the tooth. 3, The cavity in the crown of the tooth that
contains the pulp. 4, A nerve that spreads in the pulp of the tooth. 5,
An artery that ramifies in the pulp of the tooth.]

218. Each tooth is divided into two parts, namely, _crown_ and _root_.
The crown is that part which protrudes from the jaw-bone and gum, and
is covered by the highly polished enamel. The root, or "fang," is
placed in the sockets of the jaw, and consists of bony matter. Through
this bony substance several small vessels pass, to aid in the growth
and also in the removal of the tooth. There are, beside these
vessels, small white cords passing to each tooth, called _nerves_.
(See fig. 57.) When these nerves are diseased, we have the toothache.

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217. Give the structure of the teeth. What is said of the enamel? 218.
Into how many parts are the teeth divided? Describe the crown. The
root. What vessels pass through the bony matter? What is their use?

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PHYSIOLOGY OF THE TEETH.

219. The use of the teeth is twofold. 1st. By the action of the
incisors the food is divided, while the molars grind or break down the
more solid portions