LIFE OF TEETIARY PERIOD 245 



show a connection with the Proboscidea. These are that the 

 nasal opening is near the end of the snout, indicating, prohably, 

 the rudiment of a proboscis; the back of the skull is also thick- 

 ened and contains small air-chambers, the first step towards the 

 very large air-chambers of the elephant's skull, whose purpose is 

 to afford sufficient surface for the powerful muscles which sup- 

 port the weight of the tusks and trunk. The teeth show two 

 short tusks in front in the upper jaw in the same position as the 

 tusks of elephants, while the lower jaw or chin is lengthened 

 out and has two incisor teeth projecting forward. The molar 

 teeth show the beginning of the special characters which dis- 

 tinguish the huge grinding teeth of the elephants. This crea- 

 ture was named MoerWierium lyonsi; and its remains have 

 been found in great abundance along with those of both land 

 and sea animals, shoAving that they were deposited in what 

 was then the estuary of the ISTile, though now far inland. 



Somewhat later, in the Upper Eocene, another group of 

 animals, the Palseomastodons, have been found, showing a con- 

 siderable advance (see Diagram, Fig. 82). They vary in size 

 from a little larger than the preceding to that of a small ele- 

 phant. The skull is very much modified in the direction of 

 some of the later forms. After these come the Tetrabelodons 

 from the Miocene beds of France and North America, and the 

 Pliocene of Germany. These w^ere more like elephants in 

 their general form, though their greatly elongated lower jaw, 

 bearing incisor teeth, seem to be developing in another direc- 

 tion. In Tetrahelodon longirostris, however, we see the lower 

 jaw shortened and the incisor teeth greatly reduced in size; 

 thus leading on to the true elephants, in which these teeth 

 disappear. 



The skeleton of Tetrahelodon angustidens shows the lower 

 tusks sliorter than the upper ones, but in the fine specimen 

 moimted in the Paris Museum, and photographed in Sir Ray 

 Lankester's Extinct Animals, both are of the same h^igth, 

 and the upper pair curve slightly (hnvnwards on each side of 

 the lower pair; and they are thus shown in the suggested 



