32 



GEOLOGY. 



orders of animals, by being developed from behind forwards, riot from 

 beneath the tooth in wear; and the series lasted until the animal 

 attained extreme old a*e. 



They had, when young, a pair of milk-tusks (or incisor teeth) in 

 the upper jaw, and always one pair, and sometimes two pairs, of tusks 

 ■were present in the adult animal (see Figs. 1 and 4). These tusks 

 were provided with persistent pulp-cavities (analogous to the front 

 teeth of theKatand the Babbit), which continued to grow as long as 

 the animal lived. They had also three deciduous or milk-molars, and 



Fig. 3. — Skull and lower Jaw of Dinotherium giganteum (Kaup), from the Miocene of 

 Epplesheim, Hesse-Darmstadt. 



[Marked (B) on plan, and placed near the entrance to Gallery on the left-hand side.] 



one premolar, on each side, both in the upper and lower jaws, and 

 three true molars in the adult, thus making a complement of thirty- 

 four teeth during life. Some of the grinders of the Mammoth are 

 of immense size, and have as many as twenty-eight or even thirty 

 plates in a single tooth. (See Pier-case and Table-cases 17, 18 ? 

 and 19.) 



In living Elephants there are two incisors, called " tusks," in the 

 upper jaw, but the lower jaw is without incisor teeth. 



In the Dinotherium, an extinct species related to the Elephants, 



