we call "the
canines," four in all. Then we turn the corner of the mouth-front, as
it were, and come to the "grinders," cheek-teeth or molars. These are
placed in a row along each half of upper and lower jaw. In our early
mammalian ancestor they were seven in number, with broader crowns than
the peg-like incisors and canines, the bright polished enamel of the
crown being raised up into two, three or four cone-like prominences.
The back grinders are broader and bigger than those nearer the
dog-tooth. The three hindermost grinders in each half of each jaw are
not replaced by "second" teeth, whilst all the other teeth are.

[Illustration: Fig. 10.--The teeth in the upper and lower jaw-bone of
the common pig--drawn from photographs. A and B represent the right
half of the lower jaw (A) and the right half of the upper jaw (B) seen
in horizontal position. _Inc._ are the incisors or chisel-like front
teeth, three in number, in each half of each jaw and marked 1, 2, 3.
_C_ marks the canine or dog-tooth, which here grows to be a large
tusk. The molars, "grinders," or cheek teeth are marked 1 to 7. Figs.
C and D give a side view of the left halves of the upper (C) and of
the lower jaw-bone (D), with the teeth in place. The bone has been
partly cut away so as to show the fangs or roots of the teeth, which
are double in the molars, and even threefold in molar No. 7. The
explanation of the lettering is the same as that given for Figs. A and
B. The letter _p_ in Fig. B points to a "foramen" or hole in the upper
jaw-bone. These drawings are introduced here as showing the _complete_
number of teeth which the ancestor of pigs, goats, elephants, dogs,
tigers, men, and even whales possessed. The reduction in number and
the alteration in the shape of the primitive full set of teeth is
referred to in the present chapter on "Elephants," and in those on
"Vegetarians and their Teeth" (p. 102), and on "A Strange Extinct
Beast" (p. 92).]

Now this typical set of teeth--consisting of twenty-eight grinders,
four canines, and twelve incisors--is not found complete in many
mammals at the present day, though it is found more frequently as we
go back to earlier strata.[6] Though some mammals have kept close to
the original number, they have developed peculiar shape and qualities
in some of the teeth as well as changes in size. The common pig still
keeps the typical number (Fig. 10), but he has developed the corner
teeth or canines into enormous tus