The hog has fourteen _molar_ teeth in each jaw, six _incisors_, and two
_canines_; these latter are curved upward, and commonly denominated
_tushes_. The molar teeth are all slightly different in structure, and
increase in size from first to last; they bear no slight resemblance to
those of the human being. The incisors are so fantastic in form that
they cannot well be described, and their destined functions are by no
means clear. Those in the lower jaw are long, round, and nearly
straight; of those in the upper jaw, four closely resemble the
corresponding teeth in the horse; while the two corner incisors bear
something of the shape of those of the dog. These latter are placed so
near the tushes as often to obstruct their growth, and it is sometimes
necessary to draw them, in order to relieve the animal and enable him to
feed.
The hog is born with two molars on each side of the jaw; by the time he
is three or four months old, he is provided with his incisive milk-teeth
and the tushes; the supernumerary molars protrude between the fifth and
seventh month, as does the first back molar; the second back molar is
cut at about the age of ten months; and the third, generally, not until
the animal is three years old. The upper corner teeth are shed at about
the age of six or eight months; and the lower ones at about seven, nine,
or ten months old, and replaced by the permanent ones. The milk tushes
are also shed and replaced between six and ten months old. The age of
twenty months, and from that to two years, is denoted by the shedding
and replacement of the middle incisors, or _pincers_, in both jaws, and
the formation of a black circle at the base of each of the tushes. At
about two years and a half or three years of age, the adult middle teeth
in both jaws protrude, and the pincers are becoming black and rounded at
the ends.
After three years, the age may be computed by the growth of the tushes;
at about four years, or rather before, the upper tushes begin to raise
the lip; at five, they protrude through the lips; and at six years, the
tushes of the lower jaw begin to show themselves out of the mouth, and
assume a spiral form. These acquire a prodigious length in old animals,
and particularly in uncastrated boars; and as they increase in size,
they become curved backward and outward, and at length are so crooked as
to interfere with the motion of the jaws to such a degree that it is
necessary to cut off those projecting teeth, which is done with the
file, or with nippers.
[Illustration]