the most part associated together and with the pulp-cavity by
medullary canals. The calcigerous tubes radiate from those central
cavities, in all directions, with sub-parallel, diverging curvatures ;
dividing, subdividing and sending off numerous branches, which
anastomose with those of the adjoining masses, and, where these
are situated next the dentine, with the tubes of that tissue. In
each lobe of the osteo-dentine the concentric rings parallel with
the contour of the central medullary cavity, are well-marked.
Myriads of minute calcigerous cells are dispersed throughout the
osteo-dentine.
The pulp-cavity of the incisor and molar teeth of the Walrus
is filled up by a smaller quantity of the osteo-dentine. Minute
vascular canals convey the capillary blood vessels to this structure
from the vascular membrane attached to the solid base of the molars,
and, in the tusks, from the persistent pulp which fills the basal cavity.
190. Classification and analogies of the molar teeth of the Carnivora.
—The various forms of the teeth composing the molar series and their
concomitant diversity of function in the order Carnivora have led to
their being divided into distinct groups, to which the Anatomists,
who have more especially devoted themselves to the study of those
organs, have generally assigned special names. The most commonly
adopted classification and nomenclature of the molar teeth,
especially, as they exist in the Carnivora, is that proposed by
Mr. F. Cuvier in his celebrated work the ‘ Dents des Mammifères
where, treating of the ‘ machelières,’ cheek-teeth, or molar teeth,
he says : “ Ces dernières se partagent en trois divisions. La
première se compose de deux à quatre dents qui viennent après
les canines, dont l’usage est assez indéterminé, et qui sont ‘ des
fausses molaires.’ La seconde ne se compose jamais que d’une
dent qui est la carnassière ; c’est en elle que réside essentiellement
la faculté de couper les fibres de la chair. La troisième est celle
des dents tuberculeuses, dont le nombre ne s’élève jamais au-delà
de deux et qui paraissent avoir pour destination principale de
broyer les alimens susceptibles de l’être.” p. 77. The dentition
of the different genera is numerically formulised, according to the
foregoing classification: thus the genus Felis has: machelières £ ;
dont— fausses molaires, + carnassières, + -f-tuberculeuses.
In the second edition of the ‘ Leçons d’Anatomie Comparée,’
of G. Cuvier, tom. iv, 1836, the ‘fausses-molaires’ are distinguished
from the ‘ vraies-molaires,’ by their fewer roots and narrower crown :
“ par moins de racines et par une couronne moins large et conséquemment
moins propre à broyer.” (p. 246). And, in the Numerical
Tables, the molar series is divided into ‘fausses molaires rudimentaires,
fausses molaires normales, vraies molaires carnassières,’ and ‘ vraies
molaires tuberculeuses the series in Man giving :
ƒ• m- r- ^ ; /• m- n- ^ ; v-m• izi- (p - 254-)
and that in the Lion or genus Felis :—
. o -o I f. m. r. — : f. m. n. 2—-2 : v. m. c. —1 - 1: v.m . t. I —i - -i . ,( p. Zo ocAo.). J o—o * J 2—2 7 1—I 0—0 sr
Both these systems are rejected by M. de Blainville in his
‘ Ostéographie d’Animaux Vertébrés.’(l) In this beautifully illustrated
Work the molar series is divided into premolars, principal,
and true molars : * (avant molaires, principale et arrière-molaires,’
t. i, p. 43) ; which are thus exemplified in the Human dentition :
the five teeth of the molar series are divided into two premolars,
one principal, and two true or post-molars, and, with the incisors
and canine, are indicated by the following notation
“ — i. + y c. + j m. dont — av. m. y pr. — ar. m.” (1. c. p. 43)
In order to determine the analogues of these kinds of molar
teeth, and especially the ‘ principal’ molar, in other animals, the
Author gives the following definitions or characters : first, with respect
to form or shape, he divides the molars of Mammalia ‘ en avant-
molaires, en principale, et en arrière-molaires, qu’importe qu’elles
soient simples ou complex, tranchantes, ou tuberculeuses.’ (l. c. p. 43.)
As the so called principal molar of Man is not distinguished
by the trenchant, or any other peculiar form, M. de Blainville
next points out another character taken from its position in the
jaw. In most cases, he says, we may easily recognise the principal
molar, in the upper jaw, which is always the * point de départ’
(1) “ Nous avous été obligé d’abandonner cette classification des molaires des Mammifères
et d’en établir une autre.”—Ostéogr. des Mammifères, tom. i. p. 43.
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