PAL^OMASTODON. 21 



There are only two premolars in the lower jaw, the anterior Wall- 

 of the three milk-molars (figs. 9 & 13) falling out without Ctise4 ^ 

 being replaced from below ; the molars are three in number, ca ^ e 24 

 the two anterior with three transverse ridges, the third some- 

 times having in addition a small heel (fig. 10). It should be 

 noticed that in the full-grown animal all the molars and pre- 

 molars are in position and use at the same time ; it will be seen 

 that in the later forms of elephant-ancestors this is not so. 



The skeleton, so far as known, is almost exactly like that of 

 a small elephant, the only important differences being that the 

 neck is longer and the limbs most likely less massive. The animal 

 as a whole (fig. 11) must have been very like a small elephant, 

 but would be distinguishable by the longer head and neck, and 

 by the fact that instead of possessing a flexible trunk it had a 

 long snout, the lower portion consisting of the elongated lower 

 jaw, the upper without bony support and probably extending 

 beyond the lower; the projecting portion most likely was more 

 or less flexible and capable of seizing objects, and was the 

 beginning of the prehensile trunk. 



The chief steps taken by Pal&omastodon in advance ot 

 Moeritherium 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. 



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

 14), from the Lower Miocene of Northern Africa, Europe, and 41^42 

 probably Asia. This animal is as large as a medium-sized Table- 

 elephant, and its teeth and skull are much more elephant-like case 23. 

 than in Pal&omastodon. Thus the nostrils have shifted still 

 further back, and the great development of air-cells in the bones 



