PALjEOMASTODON. 19 



3. The enlargement of the second incisors in both jaws to 



form tusks. 



4. The transversely ridged character of the molars. 



5. The spout-like anterior portion of the lower jaw. 



All these characters become much more marked in the next 

 stage, which is represented by Palaomastodon from the Upper 

 Eocene of JEgypt. 



PAL^OMASTODON. 



The genus Paiteomastodon (figs. 9-11, 13 A) (Wall-case 43 ; 

 Table -case 24) is represented by species varying in size from 

 an animal little larger than Moeritherium to one nearly as 

 large as a small elephant, so that in size alone there is a great 

 advance in the direction of the modern elephants. In the 

 structure of the skull and teeth, as well as in the rest of the 

 skeleton, so far as known, the advance is likewise very striking. 



In the skull (see fig. 9) the opening of the nostril (nar.) has 



Fig. 9. 



Skull aud lower jaw of Palcco mastodon, showing the elongated chin with 

 a pair .of terminal incisors (Li.), from the Lower Oligocene of the 

 Fayum, Egypt. T ^ nat. size. 



nar., position of opening of nose ; u.i., upper second i.icisoi* or tusk. 



shifted far back from near the end of the snout, though it is 

 still in front of the orbit of the eye. The nasal bones are still 

 shorter and smaller than in Moeritherium. At the back of the 

 -skull the development of air-cells in some of the bones has 



