CHAPTER XL 



THE TEETH OF SIRENIA, HYRACOIDEA, PROBOSCIDEA, AND 

 RODENTIA. 



THE TEETH OF SIRENIA. 



MORE nearly connected with the Ungulata than with any 

 other order, but still rather widely removed from them, 

 stands the limited order of Sirenia, aquatic mammals 

 formerly termed Herbivorous Cetacea, a term rather ob- 

 jectionable, as they are not very nearly allied to the true 

 Cetacea. 



The order is now represented by two genera only, the 

 Dugongs (Halicore) and the Manatees (Manatus), but a 

 third genus (Rhytina) has only become extinct within about 

 a century. Their teeth, and other points in their organiza- 

 tion indicate that they are more nearly allied to the Ungu- 

 lata than to any other group, though their peculiarities are 

 such as to elevate them to the rank of a distinct order. 

 They are of large size, and frequent shallow water, such 

 as the mouths of great rivers, their food consisting of sea- 

 weed and aquatic plants. 



The dentition of the Dugong is in several respects a very 

 interesting one : the front part of the upper jaw, consisting 

 in the main of the intermaxillary bones, bends abruptly 

 downwards, forming an angle with the rest of the jaw. 

 This deflected end of the jaw carries two tusks, of each of 

 which the greater part is buried within the alveolus. The 

 tusk has an investment of enamel over its front and sides, 

 but on the posterior surface of cementum only, so that in 



