TOL. LXXXIX.] PHILOSOPHICAL TRANSACTIONS. 513 



could not learn, but suspect they were imported from Pegu to Calcutta, and thence 

 to London. 



The African elephant is said to be smaller than the Asiatic; yet I am credibly 

 informed, by the ivory dealers in London, that the largest tusks generally come 

 from Africa, and are of a better texture, and less liable to turn yellow, than the 

 Indian ivory, after being manufactured. This probably is owing to the tusks 

 having laid longer in Africa, before they were imported, than those brought from 

 Asia. In the latter country, most of the tusks exported are taken from elephants 

 immediately after their death ; whereas the Africans find many teeth in the desert 

 places which have been frequented by this animal. The intense heat of a vertical 

 sun will undoubtedly render the ivory firmer and harder, if the tusks happen to 

 lie on the scorching sand, or in any other dry situation. The increase of the tusk 

 arises from circular layers of ivory, applied internally, from the core on which they 

 are formed, similar to what happens in the growth of the horns of some animals. 

 When the tusks of the living elephant are sawn through, and the remaining 

 portion exposed some months to the air, this structure is clearly shown. If the 

 jteriod in which one of these circular layers is completed could be ascertained, this 

 might lead us to fix, with tolerable precision, the age of an elephant, by counting 

 the circles in each tusk. Cutting off a portion of the tusks of a living elephant 

 is a common practice; it is done with a view to make the tusks grow thicker, when 

 they are too long and slender, and also sometimes for the sake of uniformity, when 

 they grow in a wrong direction. 



In describing the structure of the grinders, it must be observed, that a grinder is 

 composed of several distinct laminae or teeth, each covered with its proper enamel; 

 and that these teeth are merely joined to each other by an intermediate softer sub- 

 stance, acting like a cement. I accordingly use the words teeth, strata, layers, and 

 laminae, as synonimous, when speaking of the structure of the grinders. The 

 structure of the grinders, even from the first glance, must appear very curious, 

 being composed of a number of perpendicular laminae, which may be considered 

 as so many teeth ; each covered with a strong enamel, and joined to one another 

 by the common osseous matter. This, being much softer than the enamel, wears 

 away faster by the mastication of the food; and in a few months after some of 

 these teeth cut the gum, the enamel remains considerably higher, so that the sur- 

 face of each grinder soon acquires a ribbed appearance, as if originally formed 

 with ridges. These strata, when first formed, have no firm attachment to each 

 other, but always appear separate and distinct, when contained in their bony 

 sockets within the jaw, after their membranes and soft parts are destroyed. Before 

 any part of a grinder cuts the gum, there is a bony crust formed above the enamel, 

 which gives a smoothness to the grinding surface. But, after the grinders cut the 

 gum, and the convex surface has been worn down a little by the trituration of the 

 food, each lamina appears to have been formed on several points*, which are covered 



* This appearance has been observed by Patrick Blair, m. d., f. u. s., who, in his Osteographia 

 VOL. XVIII, 3 U 



