862 



ANATOMY OF VERTEBRATES. 



291 



Molars, African Eler>h;int. 



into a common body of dentine. As the growth of each plate 

 begins at the summit, they remain detached and like so many 

 separate teeth or denticules, until their base is completed, when it 

 becomes blended with the bases of contiguous plates to form the 

 common body of the crown of the complex tooth from which the 

 roots are next developed. 



The plates of the molar teeth of the Siberian Mammoth (Eleplms 



primigenius) are thinner in proportion 

 to their breadth, and more numerous 

 in proportion to the size of the crown 

 than in the existing species of Asiatic 

 Elephant. In the African Elephant, 

 fig. 291, the lamellar divisions of the 

 crown are fewer and thicker, and they 

 expand more uniformly from the mar- 

 gins to the centre, yielding a lozenge- 

 form when cut or worn transversely, as 

 in mastication. From this modification 

 the gradation is close in the many extinct species to the three- 

 ridged Mastodons and two-ridged Dinotheres. 



The first molars of the Asiatic Elephant include four plates, are 

 in place and use at three months, and are shed when the elephant 

 is about two years old. 



The eight or nine plates of the second molar are formed in the 

 closed alveolus, behind the first molar by the time this cuts the 

 gum, and they are united with the body of the tooth, and most 

 of them are in use, when the first molar is shed. 



The third molar has the crown divided into from eleven to 

 thirteen plates ; it averages four inches in length, and two inches 

 in breadth, and has a small anterior, and a very large posterior 

 root ; it begins to appear above the gum about the end of the 

 second year, is in its most complete state and extensive use 

 during the fifth year, and is worn out and shed in the ninth year. 

 Its remains about this period are shown in fig. 289, d 4. The 

 three preceding teeth answer to the deciduous molars, d 2, ds, 

 and </4, in the Hyrax, fig. 287, and Hog, fig. 294. 



The fourth molar, figs. 289 and 292, m i, presents a marked 

 superiority of size over the third, and a somewhat different form : 

 the anterior angle is more obliquely abraded, giving a pentagonal 

 figure to the tooth in the upper jaw. The number of plates in 

 the crown of this tooth is fifteen or sixteen : its length between 

 seven and eight inches ; its breadth three inches. The fore- 

 part of the grinding surface of this tooth begins to protrude 



