TEETH OF DIPHYODONTS. 



335 



340, vol. ii. ( Ursus) is the development, in the lower jaw, of the 

 true molar teeth to their typical number in the placental Mam- 

 malia, and their general manifestation, in both jaws, of a tuber- 

 culate grinding surface ; the premolar teeth are much reduced 

 both in size and number. In the frugivorous Bears of India and 

 the Indian Archipelago, the four premolars (p 1-4) are commonly 

 retained longer than in the fiercer species of the northern lati- 

 tudes. In these the second lower premolar is soon lost. The 

 first true molar, m i, has a longer and narrower crown than the 

 one above. The second true molar, m 2, has a narrow, oblong, 

 subquadrate, tubercular crown, which, like that of the first true 

 molar, is supported by two fangs. The crown of the third lower 

 molar, m 3, is contracted posteriorly, and supported by two con- 

 nate fangs ; it is relatively smallest in the Sun-bears, and largest 

 in the great Ursus spelceus. The dental formula of the genus 

 Ursus is 



4 V m si = 42 (fig< 293 ' "' Ursus ^ 



It is essentially the same both in number and kind of teeth as in 



the genus Canis, but the individual or specific varieties, which in 



the Dog affect the 



true molar teeth, 



are confined in the 



Bears to the premo- 



lars. It would seem 



in the genus Ursus 



as if the preponde- 



rating size of the 



* Iff ; c \\ ' 



263 



large tubercular 

 true molars had 

 tended to blight 



o 



the development of 

 the premolars. 



In fig. 263 the 

 deciduous teeth and 

 their successors are 



riveil aS disiollVed Deciduous dentition, Bear (Ursus). 



by the removal of the outer wall of their sockets. The milk- 

 molars, four in number on each side of both jaws, progres- 

 sively increase from the first to the fourth. The character- 

 istic relative position to them of the premolars is shown at p 2, 

 3, and 4. Behind these is shown the large formative cell of the 

 first, m i, of the true molar series. 



