HISTORY OF THE PROBOSCIDEA 



423 



end and a finger-like tip, which can be used to pick up minute 

 objects. 



In the true elephants the dental formula is : i ^, c ^, p ^, to |, 

 X 2 = 14, though this formula is misleading, to the extent that 

 the milk premolars, three in number in each jaw, take the place 

 and perform the functions of the premolars, thus adding 12 to 

 the effective number of teeth. The single upper incisor on 

 each side grows into an immense tusk, which has enamel only 

 on the tip, where it is speedily worn away ; the lower jaw is 

 without incisors and there 

 are no canines above or 

 below. The grinding teeth 

 are very large and have a 

 highly complex structure 

 and a most exceptional 

 method of eruption on 

 coming into use. They 

 are thoroughly hypsodont 

 and each is composed of a 

 large number of high, broad 

 and thin plates of dentine 

 covered with enamel and 

 the spaces between the 

 enamel ridges are filled 

 with cement (see Fig. 47,. 

 p. 97) ; indeed, the whole tooth is so thickly covered with 

 cement that, when unworn, it looks Uke a mere lump, with 

 no ridges showing on the surface. The teeth increase in size 

 and in the number of component ridges from before back- 

 ward, and in the Indian species {Elephas maximus) the 

 number of ridges in the six grinding teeth, including the 

 milk premolars, is : 4, 8, 12, 12, 16, 24. In the African Ele- 

 phant ^ {Loxodonta africanus) the teeth are not so high and 

 have fewer and thicker plates, the formula being : 3, 6, 7, 7, 

 8, 10. The teeth do not succeed one another vertically in the 



Fig. 223. — Molar of the African Elephant 

 {Loxodonta a/ricanus) showing the oblique 

 mode of wear. Heavy black lines indicate 

 enamel, enclosing areas of dentine, cement 

 covering the whole tooth. 



