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OF THE NUMBEB OF TEETH. o J (
sores, commonly called Fore Teeth ; Guspidati, vulgarly called
( 'anine ; Bicvspides, or the two first Grinders ; and Molares, or
the three last Teeth. The number of each class, in each Jaw,
for the most part, is four Incisorcs, two Cuspidati, four Bicus-
pides, and four, five, or six Molares. (b)
There is a regular gradation, both in growth and form
through these classes, from the Incisorcs to the Molares, in

(b) [The permanent human dentition is indicated by the subjoined
formula:
2_2 1—1 2-2 3-3
2-2 1-1 2-2 3-3
The following is the definition and classification of teeth in diphyodont
Mammalia proposed by Professor Owen. The permanent teeth in
diphyodont Mammalia are referrible to four classes—viz., incisors,
canines, premolars (called in Man bicuspides), and molars. The terms
' incisor,' ' canine,' and ' molar' had originally reference to the shape
and office of the teeth : they are now, however, used in Comparative
Anatomy to distinguish teeth according to their relative position, connec-
tions, and development ; the latter circumstances constituting a truer
guide to the homologies of organs than shape, size, or office. The
incisors are those teeth which are implanted in the premaxillary bones
and in the corresponding part of the lower jaw. Thus the term incisor
comes to include the tusk of the Elephant, the pectinated lower front
teeth of the Flying Lemur, the broad tuberculate front teeth of some
( !arni vora. The tooth in the superior maxillary bone which is situated at
or near to the suture between it and the premaxillary, is the upper canine ;
the lower canine is that tooth which, in opposing the upper, passes in
front of its crown when the mouth is closed. The premolars are those
which succeed the deciduous molars. The permanent teeth, the most
posterior in position, which do not occupy places previously occupied
by deciduous teeth, but which are themselves a backward continuation
of the first series of teeth, being developed in the same primary groove
of the fetal gam, are the true molars.
From the dentition of early forms of both Herbivorous and Carni-
vorous Mammalia which existed during the eocene tertiary periods,
Professor Owen has been led to regard three incisors, one canine, and
seven succeeding teeth on each side of both jaws as the type formula
of diphyodont dentition. Of the seven teeth, four may be premolars
succeeding four deciduous molars, and three molars ; or there maybe
three premolars succeeding three deciduous molars, and four true
molars. The latter type of dentition is peculiar to the Marsupials and
Monotremes ; the former is the typical formula of the placental diphyo-
dont series. Amongst the few existing Mammals which have retained