TETRABELODON. 23 



The chief steps taken by Palaomastodon in advance of Moeri- 

 therium towards greater likeness to the later elephants are : 



1. Considerable increase in size. 



2. Lengthening of the snout, as shown by the mandible. 



3. Loss of canines and all the incisors except the second 



pair in both jaws. 



4. Three-ridged molars. 



5. Greater development of air-cells at back of skull. 



6. Shifting further back of the nose-opening and smaller 



size of the nasal bones. 



7. Greater similarity of the bones of the skeleton to those 



of ordinary elephants. 



TETRABELODON. 



The next stage is found in Tetrabelodon angustidens (figs. 12- 

 14, 16) (Pier-cases 41, 42; Table-case 23), from the Lower 



Fig. 12. 



Skull and mandible of Tetrabelodon angustidem, showing the greatly elongated 

 chin with a pair of terminal cutting incisors (/..), from the Lower and 

 Middle Miocene, France. ^ nat. size. 



nar.f position of opening of nose ; u.i.j upper incisors. 



Miocene of Northern Africa, Europe, and probably Asia. This 

 animal is as large as a medium-sized elephant, and its teeth and 



