222 MAMMALIAN DENTITION 



but its entire length coated with cement. There is a milk pred- 

 ecessor of this tooth but all other incisors, the canines and pre- 

 molars both temporary and permanent are non-existent. There 

 are three milk molars and three permanent molars in all but 

 only one tooth is erupted at a time. Each succeeding tooth as 

 it erupts pushes forward the worn remnant of the one in front 

 causing it to be loosened and finally shed. In the specimen 

 figured the third molar (corresponding to the first permanent 

 tooth) is erupting and the insignificant roots of the second are 

 being resorbed as the tooth becomes displaced. From the ap- 

 pearance of the teeth the Elephant is obviously a pure vegetable 

 feeder, the Asiatic species living upon grasses, the African 

 upon succulent boughs and foliage. The number of plates in 

 the six successive molars of the Indian Elephant is: 4, 8, 12 

 12, 16, 24 to 27. 



In the African Elephant the molars possess fewer plates, 

 each less compressed but with occlusal edges mammillated 

 when first erupted as in its Asiatic relative. To understand 

 the mode of evolution of the molars it is necessary to refer to 

 the extinct Mastodon in which we find not a very complicated 

 hypsodont molar but a relatively simple brachyodont tooth in 

 which the individual cusps have become united into transverse 

 lophs. Intermediate in form between the molars of Mastodon 

 and those of Elephas are the teeth of another extinct form 

 Stegodon common in the upper Pliocene of India. 



Earlier than Mastodon was a form living in Miocene times 

 Tetrabelodon by name in which the molars were SAvine-like and 

 though elongated showed cusps with commencing loph forma- 

 tion. At this stage the vertical succession normal for Mammals 

 was still present. 



Other and less advanced species have been found in the 

 Oligocene and in the Upper Eocene of Egypt. In these (Paleo- 

 mastodon and Moeritherium) the molars are simpler, less elon- 

 gated and with the usual vertical replacement. In Moeritherium 

 which existed from the Upper Eocene into the Oligocene the 

 upper molars are fairly typical trituberculate teeth with the 



