PACHYDERMATA. 



867 



transitional species, 

 extinct, such as the 

 Macrauchenia, the 



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 

 which have long become 

 Pulieotherium and the 

 Lophiodon, Coryp/iodon, 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 

 crown directed downwards and bent backwards, 



while their deeply implanted base is excavated 

 by a wide and deep conical pulp cavity, like 

 the tusks of the Mastodon and 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. 



Lower jaw of Dinothenum. 



generic name is derived.* In addition to these 

 grinding teeth the Mastodons were provided 

 with two enormous tusks, resembling those of 

 the Elephant, implanted into the intermaxillary 

 bones of the upper jaw ; and moreover those 

 Mastodons with the more simple and typical 



* Mas-re?, a nipple ; oJouj, a tooth. 



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 jaws. Of the 



3 K 2 



