426 



ZOOLOGY 



Lines of de- 

 velopment 



Mastodon 

 and mam- 

 moth 



2. So far, evolution was apparently orthogenetic, 

 the size steadily increasing, while the tusks grew longer 

 and the trunk doubtless developed. Although the 

 trunk is of course lacking in the fossils, some idea of its 

 development may be gained by a study of the surfaces 

 for muscular attachment. Now, however, while the 

 tusks became still larger, and curved upward, the lower 

 jaw or mandible reversed its former development and 

 became very short. It appears certain that the mode 

 of securing food had changed. The animal no longer 

 gained its food principally by digging or uprooting 

 plants, but used its long trunk to secure 'branches from 

 the trees or "gather in" the long herbage. The mandi- 

 ble of Tetrabelodon, if retained, would have been a use- 

 less luxury, or indeed a detriment. The teeth, now re- 

 duced in number, became extraordinarily massive, with 

 eventually a very complicated pattern of transverse 

 ridges of enamel. More powerful grinding organs could 

 hardly be imagined. The great tusks, used by the males 

 in fighting and also employed in digging, are composed 

 mainly of solid dentine, furnishing to man the familiar 

 substance ivory. The skull is short and of great height, 

 with an enormous development of the frontal sinuses or 

 air spaces. In consequence of this structure, blows on 

 the front of the head do not kill the animal, and bullets 

 fired at the forehead rarely reach the brain. The brain, 

 though small for such a large animal, is actually much 

 larger than that of man. The mental development of 

 the elephant is also noteworthy and, as in man, may be 

 connected with the ability to handle objects. Had the 

 elephant two trunks instead of one, as a man has two 

 hands, who can say what it might become ? 



3. The mastodon and mammoth are extinct ele- 

 phants. The mastodon is especially distinguished from 



