C H A P T E R VII.
TEETH OF INSECTIVORA.
T h e dental system is here remarkable for the many varieties
and even anomalies which it presents : almost the only characteris-
tic predicable of it in the numerous small quadrupeds which constitute
the Insectivorous order(l) being the presence of several sharp
points or cusps upon the crowns of the true molar teeth, which are
always broader in the upper than in the lower jaw. The teeth that
intervene between these and the incisors are most variable in form
and size, but are never absent: the incisors also differ in number,
size, and shape in different species, the anterior ones approximating
in some species to the character of the scalpriform teeth of the
Rodents.
The Insectivora are divided into the families of Moles (Talpida),
Shrews (Soricid/s), and Hedgehogs (Erinaceida:), in which succession
their dentition will be here described.
161. Talpidce.-S-Of all existing Insectivora the Chrysochlore,
or iridescent mole of the Cape, makes the nearest approach, by
the number of its molar teeth, to that remarkable condition which
was manifested in the most ancient period of mammalian existence
by the extinct Amphitherium described in the chapter of Marsupialia.
We must assign at least jpf true molars to the Chrysochlore (2) according
to their form, which, in the absence of the known order of
vertical displacement and succession, is the only character by which
the true and false molars can be defined. The anterior large lania-
riform tooth and the two succeeding small teeth are incisors, by
virtue of their position in the intermaxillary bones; the next small
(1) Pallas points out succinctly some of the leading differential characters which distinguish
the Insectivora from the Carnivora or true Ferie in his ' Zoographia Rosso-Asiatica’ where
(Vol. i. p. 119) he says Continuitate etiam dentium, numero incisorum a Ferarum Ordine
semper discordante, caninis minus elongatis, plerumque uno alterove spurio stipatis, pedum
pentadactylorum structura multifaria et singulari, clavicularum perfectarum in sceleto prsesentia,
totoque indolis, morum, victus et habitus complexu, cuncta haec genera & feris omnino discrepant,
simul affinitate concatenata inter se successive coherent.” The Insectivora are further
distinguished from the Carnivora by the absence of cerebral convolutions and by a discoid,
instead of an annular, placenta.
(2) PI. 110. fig. 1.
tooth with a simple compressed tricuspid crown is a premolar. The
crowns of the true molars are thin plates, flattened from before
backwards, with two notches on the working edge and a longitudinal
groove along the outer and thicker margin, which divides the outer
cusp into two as shown in the figure, where the middle cusp, which
is the largest, is seen in the interspace of the bifid external cusp :
the base of the lamelliform molar divides tardily into two short roots.
The third internal simple cusp is not present in the anterior molar,
and the posterior or sixth molar has a simple tricuspid crown.
Another anomaly, more remarkable than that of the shape of the
true molars, is their separation from each other by vacant intervals,
as in many Reptiles. The crowns of the five lower true molars are
compressed antero-posteriorly but are of unusual length, and have
the thicker margin turned inwards, with the summit divided by a
single notch, and the inner and lower division is subdivided into two.
The anterior incisor is small and procumbent: the second has a
larger laniariform crown; the third is small and resembles the two
premolars which intervene between this and the first true molar.
The lower molars are separated by wider intervals than those above ;
the crowns of the opposing series enter reciprocally the interspaces
and interlock : in mastication the anterior margin of one tooth works
upon the posterior margin of the opposite molar.
According to M. F. Cuvier(l) each series in the upper jaw of the
Chrysochlore includes l incisor and 9 molars; and in the lower jaw
2 incisors and 8 molars. M. de Blainville, guided by the intermaxillary
sutures in the young Chrysoclore, regards the first three teeth
in each lateral series as incisors, the fourth as a canine, and the
remaining six as molars in both upper and lower jaws. My views,
as given in the foregoing description, are expressed by the following
formula: in. |e|, pm. m. ^ = 4 0 .
In the Shrew-moles of America, (Scalops), the dentition makes
an important step towards the normal mammalian condition by the
restriction of the characters of the true molars to the three posterior
teeth in each lateral series (2) •. between these and the large
scalpriform incisor, in the upper jaw, there are six teeth, the first two
U) Dents de Mammifères, p. 63. (2) PI. 110, fig. 2.