2 6 2 BRITISH MAMMALS 



one other family of Ungulates, the Litopterna). It is, however, 

 in their teeth that elephants offer the most striking and peculiar 

 characteristics. There are no canines and no permanent pre- 

 molars. 1 The deciduous premolars (which in children of the 

 human species are lost at seven or eight years of age) last on 

 into the maturity of the animal, and they are replaced by the 

 true molars from the end that is to say, a true molar forms in 

 the bone of the elephant's jaws near the angle, and as the molar 

 pushes itself up into the gum it squeezes out the first of the 

 deciduous premolars in the anterior portion of the jaw. This 

 process is repeated by the formation and upward growth of two 

 other permanent molars, so that at last in extreme old age all the 

 three deciduous premolars have been pushed out of the skull, and 

 the elephant is grinding his food on the three permanent molars. 

 These are so large that the jaws cannot accommodate more than 

 two, and perhaps a portion of a third, at one time. These 

 molars are characterised by numerous ridges which are gradually 

 worn down in the process of mastication, while the intervals 

 are filled up with a hard cement which forms between the arches 

 of enamel-covered dentine. In the African elephants these 

 arches in the molar are arranged in a continuous diamond 

 pattern ; in the Indian elephant they form separate lozenges 

 (vide illustrations opposite). 



But the teeth of the elephant which are most interesting to 

 the scientific observer are the tusks. These are incisor, or front, 

 teeth, and, judging from what we see in the Mceritherium^ they 

 represent the two middle incisors, not the first or the third in 

 the series. These incisors in existing elephants are only de- 

 veloped, one on each side, in the upper jaw. In some of the 

 earlier mastodons, however, there were incisors (tusks), fairly 

 long or quite rudimentary, in the lower jaw as well ; while in 

 the extinct Dinotherium the incisors of the upper jaw had 

 apparently dwindled away completely, while the pair in the 

 lower jaw had developed into strong tusks. In the mastodons 



1 Permanent premolars occasionally make their appearance in a very 

 reduced form, and without functional capacity in extinct species of elephant. 



