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TEETH OF THE VERTEBRATA. 485

have a normal direction. It is said that castration arrests the excessive
development of the tusks of the boar, just as this operation profoundly
affects the growth of the antlers of the deer—a circumstance which at
once relegates the cause of this condition to sexual influences.
The first premolar has no deciduous predecessor, and disappears soon
after the adult stage is reached. The rest of the premolars increase in
complexity and size from front to rear, but none of them are quadri-
tubercular. The first and second molars are quadrate in section, with
four-lobed crowns. The last molar is greatly elongated in an antero-
posterior direction, which is occasioned by the possession of an enormous
heel, much as in the bears, and its crown, as in the others, besides pre-
senting the normal four cusps, has an immense number of subsidiary
tubercles, giving to it a decidedly wrinkled appearance.
In the wart-hogs (Phacochcenis) a very peculiar modification of the
molar pattern is to be seen in the last tooth. In the unworn state the
crown of this tooth presents about thirty small tubercles, arranged in
three rows in a direction longitudinal to the axis of the body, the inter-
mediate spaces between them being occupied by cementum. When wear
takes place, the summits of these cusps are abraded, leaving as many
little dentine islands bordered by enamel; they are strengthened by the
addition of cement.
The canines are of enormous size, devoid of enamel, and grow^ from
persistent pulps ; the suj)erior ones are directed upward at first, piercing
the upper lip, and then curve backward toward the eye; their length is
sometimes as much as eight or ten inches. All the molar teeth are gen-
erally shed in old age, with the exception of the fourth premolar and
the last true molar, so that the molar dentition is practically reduced at
this time to four upon each side in both jaws, and is the only case of
the kind known in the Mannnalia.
The peccaries constitute another family of this division, and are
known from the lowest Miocene, if not from the Upper Eocene depos-
its. Their molar dentition is more nearly like that of the Condylarthra
and ])rimitive perissodactyles than other suillines, lacking, as a rule, the
great development of the minor tubercles of the molars of the hog as
well as the elongated heel of the tooth. The canines, moreover, are nor-
mal in direction, and the great disparity in size between these teeth does
not exist in the sexes. The incisors are of the usual pattern, although
the outer pair is absent from both jaws in some genera.
From this family the transition is easy to the earlier forms of the
selenodonts, in Avhich the feet were multidactyle ; in one genus, Oreodon,
as has been recently shown by Prof W. B. Scott, the anterior limb was
provided with the normal number of toes, five. That family, which
almost completely bridges the chasm between these divisions, is the
extinct Anthracotheridce, whose remains are abundant in the Miocene
strata of Europe, but less so in this country.
It is somewhat uncertain how many genera should be referred to
this family, and by what character or characters it should be defined.
Palceoclioeru^, which by common consent is a suilline, has four lobes upon
the crowns of the superior molars, which are conic and not connected
with an external rib, together with two small intermediate cusps, repre-