710 ELEPHANTS xxix. 4 



economy of energy, though to do this they must eat throughout a 

 large part of the day, perhaps for as much as 18 hours. Here another 

 factor has to be considered, namely, the area of tooth available for 

 grinding the food. This will vary approximately as the two-thirds 

 power of the total weight; as the animals become larger the tooth 

 surface needs therefore to be relatively increased. 



Fig. 473. Section of tooth of elephant. The front part of the 



crown (on the left) is already worn away. Notice the upstanding 



enamel lamellae, which reach to the base of the tooth. Dentine 



is shown dotted, cement by lines (From Weber.) 



With these factors in mind we shall recognize that the significant 

 features in the organization of elephants are that they are very large 

 animals, with an efficient nervous organization for finding the food, 

 efficient means of collecting it, and large surfaces for grinding it. 



The trunk is the main means of collection — an enormously elongated 

 nose and upper lip, with appropriate muscles and sensitive grasping 

 tip. The muscles have been developed chiefly from the parts of the 

 facial musculature that are responsible for moving the sides of the 

 nose. The trunk probably developed rather quickly, in late Miocene 

 times, perhaps 10-15 million years ago; the earlier elephants of the 

 Miocene possessed very long lower jaws, which became shortened 

 as the trunk developed. Any tall animal must have means of reaching 

 the ground and the trunk is probably superior even to a very long 

 neck for this purpose, because it can reach upwards and sideways as 

 well as downwards. 



Only one pair of continually growing incisors remains in modern 



