PACHYDERMATA. 
adult Rhinoceros no traces of canine teeth are 
visible, but Professor Owen succeeded in de- 
tecting their existence in a rudimentary condi- 
tion in the mature fetus of the Rhinoceros 
Indicus, although both the teeth and their 
sockets disappear at a very early age. 
The vast hiatus which in the series of existing 
Mammals divides the Rhinoceros from the 
Tapir, and this from the Elephant, was once 
filled up by interesting transitional species, 
which have long become extinct, such as the 
Paleotherium and the Macrauchenia, the 
Lophicdon, Coryphodon, and others requiring 
no particular notice in this place. But that 
most extraordinary of extinct Pachyderms, the 
Dinotherium, must not be so lightly passed 
over, inasmuch as its dentition appears to have 
been quite unique in character, as may be seen 
on reference to fig. 478, which represents the 
lower jaw of this gigantic quadruped. From 
this it will be seen that the molar and premolar 
teeth resemble in some respects those of the 
‘Mastodon; but the great peculiarity of the 
Dinotherium exists in its tusks projecting from 
the lower jaw. These tusks are two in number, 
implanted in the prolonged and deflected sym- 
physis of the lower jaw, in close contiguity 
with each other, and having their exserted 
_erown directed downwards and bent backwards, 
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while their dee ly implanted base is excavated 
by a wide and™deep conical pulp cavity, like 
the tusks of the Mastodon an Elephant, No 
such tusks nor germs of such have yet been 
discovered in the upper jaw, so that it is highly 
probable that this gigantic Pachyderm was of 
aquatic habits, like the Hippopotamus, and 
that its tusks served to detach and tear up by 
the roots the aquatic plants upon which it fed, 
as well as for weapons of defence or combat. 
No family of Mammalian Quadrupeds has 
suffered more from the destructive operations 
of time than that of the Proboscidian Pachy- 
dermata. Two species only, the Indian and 
the African Elephants, continue to represent 
this type in the Mammalian series of the 
present day; whilst those that manifested the 
modifications of the dental system which gra- 
dually reduce the complexity of the Elephantine 
dentition to the comparative simplicity of that 
of the Dinothere and Tapir, have long since 
-been blotted out of the series of living beings. 
Of these the gigantic Mastodons are the most 
conspicuous — animals nearly allied to the — 
existing Elephants, but differing from them in 
the construction of the grinding surfaces of 
their molar teeth, which had their crowns 
studded with conical eminences more or less 
resembling the teats of a cow—whence the 
Fig. 478. 
generic name is derived.* In addition to these 
_ gtinding teeth the Mastodons were provided 
| with two enormous tusks, resembling those of 
the Elephant, implanted into the intermaxillary 
§ of the upper jaw; and moreover those 
_ Mastodons with the more simple and typical 
‘ 
* Mactis, a nipple; dois. a tooth. 
j 
, 
Lower jaw of Dinothertum. 
molar teeth likewise manifest the Dinotherian 
character in having tusks in the lower jaw of 
the adult male and in the young of both sexes. 
The dentition of the Elephant, the sole 
surviving genus of the great Proboscidian family, 
consists. of two long tusks, one situated in 
each of the intermaxillary bones, and of large 
and complex molars in both jaw. Of the 
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