d. The characters of
the sectorial teeth deserve special attention, as, though fundamentally
the same throughout the group, they are greatly modified in different
genera. The upper sectorial is the most posterior of the teeth which
have predecessors, and is therefore reckoned as the last premolar (p. 4
of the typical dentition). It consists of a more or less compressed
blade supported on two roots and an inner lobe supported by a distinct
root (see fig. 1). The blade when fully developed has three cusps (i, 2
and 3), but the anterior is always small, and often absent. The middle
cusp is conical, high and pointed; and the posterior cusp has a
compressed, straight, knife-like edge. The inner cusp. (4) varies in
extent, but is generally placed near the anterior end of the blade,
though sometimes median in position. In the _Ursidae_ alone both the
inner cusp and its root are wanting, and there is often a small internal
and posterior cusp (5) without root. In this family also the sectorial
is relatively to the other teeth much smaller than in other Carnivora.
The lower sectorial (fig. 2) is the most anterior of the teeth without
predecessors in the milk-series, and is therefore reckoned the first
molar. It has two roots supporting a crown, consisting when fully
developed of a compressed bilobed blade (1 and 2), a heel (4), and an
inner tubercle (3). The cusps of the blade, of which the hinder (2) is
the larger, are separated by a notch, generally prolonged into a linear
fissure. In the specialized _Felidae_ (I) the blade alone is developed,
both heel and inner tubercle being absent or rudimentary. In _Meles_
(V) and _Ursus_ (VI) the heel is greatly developed, broad and
tuberculated. The blade in these cases is generally placed obliquely,
its flat or convex (outer) side looking forwards, so that the two lobes
or cusps are almost side by side, instead of anterior and posterior. The
inner tubercle (3) is generally a conical pointed cusp, placed to the
inner side of the hinder lobe of the blade. The special characters of
these teeth are more disguised in the sea-otter than in any other
species, but even here they can be traced.

[Illustration: FIG. 2.--Left lower sectorial or carnassial teeth of
Carnivora, I, _Felis_; II, _Canis_; III, _Herpestes_; IV, _Lutra_; V,
_Meles_; VI, _Ursus_. 1, Anterior cusp of blade; 2, posterior cusp of
blade; 3, inner tubercle; 4, heel. It will be seen that the relative
size of the two roots varies