ble size, as appears in the cut representing teeth at
birth. During the second week, a tooth will usually be added on each
side, and the mouth will generally appear as in the next cut; and before
the end of the third week, the animal will generally have six incisor
teeth, as denoted in the cut representing teeth at the third week; and
in a week from that time the full number of incisors will have appeared,
as seen in the next cut.

[Illustration: THREE WEEKS.]

[Illustration: MONTH.]

[Illustration: FIVE TO EIGHT MONTHS.]

[Illustration: TEN MONTHS.]

[Illustration: TWELVE MONTHS.]

[Illustration: FIFTEEN MONTHS.]

These teeth are temporary, and are often called milk-teeth. Their edge
is very sharp; and as the animal begins to live upon more solid food,
this edge becomes worn, showing the bony part of the tooth beneath, and
indicates with considerable precision the length of time they have been
used. The centre, or oldest teeth show the marks of age first, and often
become somewhat worn before the corner teeth appear. At eight weeks, the
four inner teeth are nearly as sharp as before. They appear worn not so
much on the outer edge or line of the tooth, as inside this line; but,
after this, the edge begins gradually to lose its sharpness, and to
present a more flattened surface; while the next outer teeth wear down
like the four central ones; and at three months this wearing off is very
apparent, till at four months all the incisor teeth appear worn, but the
inner ones the most. Now the teeth begin slowly to diminish in size by
a kind of contraction, as well as wearing down, and the distance apart
becomes more and more apparent.

[Illustration: EIGHTEEN MONTHS.]

From the fifth to the eighth month, the inner teeth will usually appear
as in the cut of the teeth at that time; and at ten months, this change
shows more clearly, as represented in the next cut; and the spaces
between them begin to show very plainly, till at a year old they
ordinarily present the appearance of the following cut; and at the age
of fifteen months, that shown in the next, where the corner teeth are
not more than half the original size, and the centre ones still smaller.

[Illustration: TWO YEARS PAST.]

The permanent teeth are now rapidly growing, and preparing to take the
place of the milk-teeth, which are gradually absorbed till they
disappear, or are pushed out to give place to the two permanent central
incisors, which at a year a