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THE POPULAR SCIENCE MONTHLY, 



ing the incisors, or front teeth, and the molars, or grinders ; while the 

 front teeth themselves only exist in.the upper jaw. The incisors grow 

 from "permanent pulps," and hence they increase during the whole 

 life of the animal, or nearly so. A large pair of tusks may weigh from 

 one hundred and fifty to two hundred pounds, and as regards struct- 



Fig. 2. Vartotjs Uses or the Proboscis. 



ure they are found to consist of dentine, or " ivory," and of " cement * ; 

 while the enamel, which forms such a characteristic feature of ordi- 

 nary teeth, may or may not be represented. The tusks vary, according 

 to Darwin, " in the different species or races according to sex, nearly 

 as do the horns of ruminants. In India and Malacca, the males alone 

 are provided with well-developed tusks. The elephant of Ceylon," 

 adds Mr. Darwin, " is considered by most naturalists as a distinct race ; 

 there, ' not one in a hundred is found with tusks, the few that possess 

 them being exclusively males.' The African elephant is undoubtedly 

 distinct, and the female has large, well-developed tusks, though not so 

 large as those of the male." The molars, or grinding-teeth, exhibit an 

 equally curious structure. In the life-time of an elephant twenty-four 

 molar teeth are developed in all, six on each side of each jaw. But, 

 at any one time in the life of the animal, not more than two of these 

 teeth are to be seen in each side of the jaw. A curious succession of 

 these molars takes place in the elephants, for they are found to move 

 from behind forward, the teeth in use being gradually ousted from 

 their place by their successors as the former are worn away. Thus 

 the whole "set of molars in due time moves forward in the jaw and 

 each successive tooth is, as a rule, larger than its predecessor. In 

 structure, the molars of the elephant are highly peculiar, each exhibit- 

 ing the appearance rather of a compound than of a single tooth. Each 

 tooth is built up of a series of plates set perpendicularly in the tooth, 

 and consisting of ivory, or " dentine," covered by enamel, while " ce- 

 ment " fills up the interspaces between the plates. As the tooth wears 

 in its work, the enamel comes to project above the surface of the tooth, 



