220 IVORY AND THE ELEPHANT 



tissue exceptionally tough and elastic.* When ivory de- 

 composes it disintegrates along the lines of the concentric 

 interglobular spaces, and fossil ivory in this state presents 

 the appearance of a series of detached concentric rings. f 



Occasionally the grinders of elephants have been worked 

 as ivory, but their triple composition of enamel, dentine, 

 and cement renders them difficult to cut, and they do not 

 yield a material sufficiently homogeneous to constitute a 

 satisfactory substitute for true ivory from the tusk.| Wal- 

 rus teeth and the tusk of the narwhal have also been used, 

 the former to a certain extent by dentists. The latter were 

 the famous unicorn's horns of past centuries, and are now 

 rather kept as curiosities than turned into material for the 

 useful or ornamental arts. 



The characteristic appearance presented by a cross-section 

 of ivory, the series of curved lines produced by a bending 

 of the tubules constituting the dentine, is first observa- 

 ble in the palseontological series leading up to the modern, 

 in the case of the large upper tusks of Tetraholodoii angusti- 

 dens from the Lower Miocene of Northern Africa, Europe, 

 and probably Asia;** the exceptionally large lower tusks of 

 some American Tetrabolodonts show the same formation. 



The dentition of the elephant is very characteristic and 

 peculiar. The first tusks (developed incisors) are shed, 

 and are replaced by a second growth, which remains, in- 

 creasing gradually in length and weight until the animal's 

 death. The molars, however, are renewed no less than 

 five times in the course of the elephant's life. Only four 



*W. B. Carpenter, "The Microscope and Its Revelations," 7th ed., London, 1891, p. 

 948; see also Professor Owen, in Journal of the Society of Arts, Vol. V, pp. 65-70; Decem- 

 ber 19, 1856. 



fCharles S. Tomes, "A Manual of Dental Anatomy," 3rd ed., London, 1889, p. 373. 



JHoltzapffel, op. cit.. Vol. I, p. 139. 



**Andrews, "A Guide to the Elephants (recent and fossil) in the British Museum," 

 London, 1908, pp. 23, 24. 



