Page 104 - My FlipBook

88 HUNTER ON THE TEETH. —
dinal groove. These fangs at their middle, are generally bent a
little backwards.

between the angles give a grooved appearance to the outer surface of
the molar series in Scalops. In the common Mole (Talpa Europcea), the
normal number of teeth is retained : there are four premolars and three
true molars on each side, both above and below. In the upper jaw, the
three first premolars have small, simple, conical crowns, and are implanted
by two fangs ; the fourth premolar has a large trihedral crown, and three
fangs. The true molars are multicuspid. The middle one is the largest;
it is quinque-cuspid, with usually four fangs ; the third, which is the
smallest, has a tricuspid crown and three fangs. In the lower jaw, the
first premolar is the largest. Each lower premolar is implanted by two
fangs, and lias a small posterior talon at the base of the conical crown.
The lower true molars, of which the middle is the largest, are quinque-
cuspid, and implanted by two fangs. In the Solenodon of Hayti, a species
allied to the Shrews (Sorex) and Water-moles (Mygale), seven teeth suc-
ceed the incisors in both jaws. Of these, in the upper jaw, the two
anterior have trihedral conical crowns ; the five succeeding present, in
addition, an external, tuberculate basal ridge. In the lower jaw, the
four last teeth have multicuspid crowns. The typical Shrews (Sorex)
have two small, and three large, multicuspid molars in the lower jaw
:
in the upper, the uumber of premolars is variable. The last true molar
is usually of small size. The differences in the number of teeth in the
upper jaw, together with the variations in the shape of the large incisors,
are points which serve to characterise the sub-genera of Shrews. The for-
mula of the molar series in the Tupaias (Glisorex) iap £ £ \ m^f'. The
.'
premolars increase in size and complexity as they approach the molars
:
the two first of the latter in the upper jaw have each six cusps, the
corresponding teeth in the lower jaw are quinque-cuspid The last true
molar, both above and below, is the smallest, and has three cusps. The
Gymnure is one of the rare instances among existing Mammals in which
the typical dental formula is retained. It has four premolars and three
true molars on each side in both jaws. In the upper jaw, the first three
premolars have simple crowns—the last is large and quadricuspid. The
first and second upper true molars present square and multicuspid
crowns. The third is smallest and triangular. In the lower jaw, the
third and fourth premolars are much larger than the first and second
;
the fourth is tricuspid. In the European Hedgehog {Erinaceus Europceus)
The
there are four superior premolars on each side, and two inferior.
true molars are three on each side, both above and below. The last
premolar in both jaws is the largest : above, it is quadricuspid, with
three fangs ; below, it has a sub-compressed tricuspid crown, with two
fangs. Both upper and lower true molars decrease in size from the first
to the third. The first and second above are quadricuspid, the corre-
sponding teeth below are narrower and quinque-cuspid. The tropical