ON THE TEETH OF MAMMALIA. 



115 



with flat broad edges, or surfaces, opposing each other, a central depression 

 shewing itself as each tooth is worn. In the Hog they are strong ; those 

 113 of the lower jaw projecting obliquely. 



In the Hippopotamus (fig. 113) those 

 of the upper jaw are conical, and pro- 

 ject downward ; those of the lower jaw 

 horizontally, the two middle being ex- 

 tremely developed, long, and cylindrical. 

 In the Elephant there are no incisors in 

 the lower jaw ; and the two in the 

 upper assume the form of huge, cylin- 

 drical, recurved tusks, without a true 

 root. On the contrary, in that fossil 

 animal, the Dinotherium (an aquatic pa- 

 chydermatous animal), the incisors of the 

 Teeth of Hippopotamus. lower jaw sweep abruptly downward, 



like the tusks of the Elephant, resembling them in shape (excepting that 

 they are rather incurved), and almost equalling them in magnitude. 



114 The Rodentia have large curved inci- 



sors, see the annexed figure (114), of the 

 mouth of the Capybara, without true roots, 

 with scalpriform, or chisel-like edges, of 

 great sharpness. The Edentata are desti- 

 tute of incisors. Among the marsupial 

 animals the true Opossums have ten inci- 

 sors above, and eight below ; the Dasyuri, 

 of Australia, have eight above, and six 

 below; the Phalangers (Phalangista, Geoff.) 

 have six incisors above, and two large pointed oblique incisors below, 

 as have, also, the Petauri and the Kangaroos. 



The Wombat closely resembles the Rodentia, and has two incisors 

 in each jaw. The Cetacea have no incisors ; nor, indeed, can the teeth, 

 with which the jaws of certain groups (as the Dolphin, Porpoise, &c.) 

 are furnished, be called either by the term canine or molar : they are 



Incisors of Capybara. 



conical, prehensile, or seizing teeth, interlocking when the jaws are 

 closed, as in fig. 115, which represents the jaws of a Dolphin. There is, 

 however, one exception ; the Narwhal (Monodon), destitute of other teeth, 



