280 TEETIT OF THE ELEPHANT. 



molar has been thus worn clown to a uniform surface, it 

 becomes useless as an instrument for grinding tlie coarse 

 vegetable substances on which the elephant subsists ; it is 

 attacked by the absorbent action, and the wasted portion 

 of the molar is finally shed. 



The grinding-teeth of the elephant progressively increase 

 in size, and in the number of lamellar divisions, from the 

 first to the last; they succeed each other from behind 

 forwards, moving not in a right line, but in the arc of a 

 circle, shown by the curved line in Fig. 73. The position 

 of the growing tooth in the closed alveolus, ?/z, 5, is almost 

 at right angles Avith that in use, the grinding surface being 

 at first directed backwards in the upper jaw, and forwards 

 in the lower jaw, and brought by the revolving course 

 into a horizontal line in both jaws, so that they oppose 

 each other when developed for use. The imaginary pivot 

 on which the grinders revolve is next their root in the 

 upper jaw, and is next the grinding surface in the lower 

 jaw; in both,, towards the frontal surface of the skull. 

 Viewing both upper and lower molars as one complex 

 whole, subject to the same revolving movement, the sec- 

 tion dividing such whole into upper and lower portions 

 runs parallel to the curve described by the movement, 

 the upper being the central portion, or that nearest the 

 pivot; the lower, the peripheral portion. The grinding 

 surface of the upper molars is consequently convex from 

 behind forwards, and that of the lower molars concave; 

 the upper molars are always broader than the lower ones. 

 The bony plate forming the sockets of the growing 

 teeth is more than usually distinct from the body of the 

 maxillary, and participates in this revolving course, ad- 

 vancino: forwards with the teeth. 



