870 
these different operations are by no means 
equally in progress in all points of the tooth at 
the same time, but they occur much earlier in 
front than behind; so that the anterior lamine 
= be already consolidated by their summits 
and even by their bases while the bases of the 
middle ones remain separate, and when the 
posterior lamine are not even formed, or only 
represented by the patches of ivory that are 
first deposited upon the apices of the pulps. 
There was formerly much discussion as to 
the number of grinding teeth proper to the 
Elephant, and as early as 1715 the Royal 
Society of London observed that there is 
sometimes only one and sometimes two on 
each side in either jaw, and moreover that the 
first tooth is longer or shorter in proportion to 
the second in different individuals. Pallas first 
explained the real mode of the succession of 
these teeth, accounting for all these irregu- 
larities, and showing that the Elephant has at 
first only a single tooth on each side, until a 
second, developing itself, replaces the first, so 
that during a certain period there are two, until 
the shedding of the first again leaves only one, 
Cuvier first announced that this succession and 
consequent alternate change in the number of 
the teeth was repeated more than once, because 
he found the detached germs of a third grinder 
in the jaw of an Elephant, with two teeth in 
situ. 
It thus becomes easy to understand how the 
grinding teeth of the Elephant, notwithstanding 
the enormous wear to which they are perpetually 
subject, are kept constantly ready for use, and 
renovated in front as fast as they are worn away 
behind. No sooner has the body of the first- 
formed tooth pierced the gums than it begins to 
undergo important changes. As the Elephant 
is herbivorous, its teeth are necessarily worn 
away by mastication like the teeth of all other 
herbivorous animals, a circumstance which is 
indeed necessary in order that the grinding 
surface may be constantly kept in a condition 
‘to bruise vegetable substances. The little in- 
dentations on the tops of the lamine are first 
worn off, until the wearing down has reached 
the interior of the tooth, when each denticle of 
course presents an oval disc of ivory, surrounded 
by a ring of enamel and enclosed in the ce- 
mentum, three substances, which, being of very 
different degrees of hardness, are ground away 
unequally, so as always to present a rough 
grinding surface like that of a mill-stone. 
The tooth, moreover, by its rhomboidal figure 
and very oblique position in the jaw, presents 
its anterior portion above the gums long before 
the posterior, so that the surface produced by 
mastication forms an obtuse angle with the 
plane of the upper surface of the tooth: hence 
it happens that when the front of the tooth is 
deeply worn away, the middle lamine are 
scarcely used at all, and the hinder ones remain 
quite intact, tera the summits of the 
indentations of their crowns under the form of 
little round eminences. In the same way the 
anterior denticles are altogether destroyed before 
the posterior are very far worn down, a circum- 
stance which explains another phenomenon 
PACHYDERMATA. 
which is peculiar to the Elephant, viz. that its 
teeth diminish in length at the same time that 
pm Bo worn away in depth. ” 
hilst the exposed part of the tooth is thus 
worn away, that part of the root which corre- 
sponds with the portion ground down is re- 
moved by a very different process. When — 
examined under these pte am the er! 
of the anterior denticles have the He 
being eaten away as by a kind of caries, so 
that all the front of the tooth is thus re 
when the grinding surface has ceased to be 4a 
efficient, and the tooth, when about to be shed, — 
is reduced to a very small size, however large 6 
it might have been originally. 
The tooth which is in use is therefore per- — 
tually moving forward in consequence of this 
paree and making room for that which is in — 
progress of formation in the hinder part of the — 
jaw to succeed it. This latter, in turn, by its” 
development assists in pushing the first for- 
wards, so that it is strictly true that in the 
Elephant the second set of teeth grows behind 
the milk set, instead of above or below them, 
as in other animals (fig. 479). 
The tusks of the Elephant are very differe 
in their structure from the molar teeth, cot 
sisting of two substances only, the ivory @ 
the enamel. These tusks grow during tf 
whole life of the animal, and sometimes att 
enormous dimensions, measuring eight or ni 
feet in length, and weighing upwards of t 
hundred pounds. In the females of the Asiat 
Elephant the tusks are very small, but in 
African Elephant both sexes have these 
largely developed. These remé et 
which are evidently the representatives of 
enormous tusks bestowed on some of the { 
cea, such for example as the Narwal ( Mi 
don ), are implanted in enormous sockets 
iy the intermaxillary bones of the t Le! 
he central portion of each tusk, the # 
which forms by far the greatest pe ) 
tooth, is secreted by an enormous pulp 10 
in a deep cavity which is excavated Im 
from the surface of which it is deposited” 
by layer in successive strata. ne pul 
nucleus from which the mass of the too 
thus formed has not the slightest organi 
nection with the ivory which has bee 
product of its secretion; not a fibre or’ 
or even the slightest cellulosity p 
one to the other. The tusk is therefore 
kept in its socket by the tight embrace of 
parts around it, and its direction may be re 
changed by gentle and continued pressut 
» 
the same way as dentists succeed in chan 
wr 
