224 MAMMALIAN DENTITION 



its inner and outer aspects. The anterior cheek teeth are lost 

 as the posterior ones come into place so that only two molars 

 remain on each side in older specimens. 



It is obvious then that the Dugong has undergone reduction 

 in number and functional capacity of the antemolar teeth. The 

 Manatee on the other hand is a terminal form illustrating tooth 

 differentiation of a quite different character: in it we see actual 

 increase in the number of molars as we have already noted in 



Fig. 80. — Dentition of Dugong (Halicore australis?, Oberlin College Collection). 

 In this skull of an adult female note the i educed dentition, the simplified hypsodont 

 cheek teeth and the site of rudimentary anterior teeth on the symphysis. 



certain other highly specialized Mammals, the Armadillos and 

 certain Cetacea for example. There is no doubt that such 

 increase in number of molars may and does occur in mam- 

 malian orders though of the causes which bring it about we 

 are completely ignorant. 



In spite of the fact that the modern Sirenians are so very 

 specialized we know enough of their ancestral history to state 



