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TEETH OF THE VERTEBRATA. 437

they are implanted in both jaws, and contrast with tlie graceful curve
they pursue in the normal human mouth.
The median pair of incisors are larger both above and below ; in the
upper jaw they are more than twice. the size of the lateral pair, Avhile in
the lower jaw they are more nearly equal. Between the lateral pair
and the canine above there is a. considerable space, into which the lower
canine bites. The canines are relatively large, and their apices rise far
above the level of the surrounding teeth. They are imperfectly trihe-
dral in form, with a trenchant edge behind. These teeth are larger in
the male than in the female.
The premolars or bicuspids differ from those of man in the upper
jaw in being implanted by three roots like the molars ; their crowns
are very similar to those of man, presenting essentially the same ele-
ments. The pattern of the crowns of the molars is like that of the
human subject both above and below, but the last molar is as large as
it is implanted by three roots, and is always perfectly formed.
the others ;
In the lower jaw the two posterior molars slightly exceed the first in
size, and the last is distinctly five-lobed. The first lower premolar is
two-rooted, and has a faint resemblance to the corresponding tooth in
the baboons. The second is also implanted by two roots, and its crown
agrees with that of man.
In the other genera minor differences only are to be met with in the
form, pattern, and arrangement of these organs.

The Human Dentition.
In this connection we come next to consider the teeth of man ; and
before so doing I am constrained to make some general remarks in
regard to the position he occupies in the zoological scale. While it is
undeniable that by virtue of his superior brain-capacity and intellectual
development man is to be accorded a place at the head of the animal
kingdom, it is nevertheless true that much of his anatomical structure
has not been specialized beyond that of many of the lower forms. The
fact that different members of the mammalian sub-class have been mod-
ified in different directions, some to fit one environment and some
another, has led to the specialization of different sets of organs, and
that, moreover, in different ways as the surrounding conditions and
particular exigencies of the case have required.
It is these differences which enable the naturalist to construct zoologi-
cal definitions of the major or minor groups, such as orders, sub-orders,
families, genera, etc. The impracticability of determining which ani-
mal is highe.^^t or lo^west in the scale of organization is thus rendered
apparent from the fact that a comparison of different sets of organs is
involved. Thus, in their dental, digestive, and limb structure the
ungulates surpass all other Mammalia in complexity and specialization,
and in these respects may be said to be highest, wdiile in the matter of
brain-development they are much inferior to others. The monkey line
or Primates, on the other hand, of which man is at the head, retain a
comparatively generalized structure of the limbs, teeth, and digestive