6 



ELEPHANTS, EECENT AND EXTINCT. 



also to the single pair of sucli teetli in the Eodents 

 (rats, hares, &c.). Moreover, these teeth, like the ineisors 

 of the Rodents, grow continuously throughout the life 



of the animal, 

 owing to the cir- 

 cumstance that 

 the pulp-cavity 

 at their base 

 always remains 

 open, and has a 

 permanent con- 

 nection with the 

 soft structures 

 of the gum. In 

 our own teeth, 

 on the contrary, 

 the pulp-cavity 

 closes at a cer- 

 tain period, after 

 Avhich there is a 

 total cessation of 

 growth. These 

 ever - growing 

 tusks of the 

 elephants are 

 preceded in the 

 voung animal by 

 a pair of small 

 milk-tusks, with 

 a closed pulp- 

 cavity, which are 

 shed at an early 

 period of life. 

 In both of the 

 living species of 

 elephant the 

 tusks are con- 

 fined to the 

 upper jaw ; but whereas they occur in both sexes in the 

 African elephant, in the Indian species large permanent 



Fig. 



4.— Last or Sixth Upper Molar Tootli of 

 a Mastodon ; half natural size. 



