ON THE BONES OF THK MASTODON. 841 



■Sad. The tusks of the elephant are enveloped with a substance 

 which dilTers from ivory in its texture ; its fibres converge towards the 

 centre, and though the substance is not so hard as common enamel, 

 it is nevertheless a species of it. 



" The band of the circumference," says Daubenton, " is sometimes 

 composed of straight transverse fibres, which would terminate in the 

 centre if prolonged." — (Natural History, vol. xi, 4to.) 



This, liowever, is an observation v/hich any one may make upon the 

 tusks, when their surface has not been impaired. My tusk of the mas- 

 todon resembles those of the elephant in this particular. 



3dly. Perhaps the softness of the interior of the tusks found by Mr. 

 Peale may be owing to some accidental cause which may have decom- 

 posed them more or less, although the bones discovered at the same 

 time had scarcely undergone any alteration. M. Morichini, professor 

 of chemistry at Rome, ascertained, some }'^ears since, that fossil ivory is 

 liable to decomposition by changing {by what agency has not been dis- 

 covered) its phosphate of chalk into fluid of chalk. 



Our complete tusk of the mastodon has not any fluoric acid, as MM. 

 Vauquelin and Laugier, who have analysed it, have ascertained. Per- 

 haps the tusks of Mr. Peale have some. 



The curves of these tusks vary as much as do those of the elephant. 

 That which is represented by M. Micliaelis is almost straight ; my own, 

 M'hich I give in plate 22, fig. 3, is gently arched. A very large one, 

 found with the head of the skeleton of Philadelphia, is curved almost to 

 a semicircle. As it was much mutila,ted, they were under the neces- 

 sity of substituting a model in wood in its place. Following the line 

 of the circumference, it measures Z,\1 in length. That sent by Mr. 

 Jefferson is 2,35, or more than seven feet in length, and 0,194 in 

 diameter at the base. 



The alveoli of the skeleton of Mr. Peale are eight inches English, 

 or 0,202 in depth ; the points of the tusks which fit into them are not 

 qmte in the same place as the base, and form the commencement of a 

 worm screw. It would appear that their direction on emerging from 

 the sockets is a little more oblique in front than in the elephant. At 

 first they were placed, as they appear in the elephant, with the point 

 "Sjpwai'ds. In this position tiie distance between their bases was 6", or 

 0,15, and 8^ d'^ or 2,65 between their points'*. 



M. Rembrandt Peale afterwards determined upon placing them in 

 an inverted position — that is, with the convexity in front, and the 

 points downwards and backwards. He gives the following motives for 

 this change f: — ■ 



1st. The depression of the occipital condyle, and the very decided 

 curve of the tusks, elevated the points of the latter to too great a height 

 above the ground, and above the head of the animal itself. It could 

 never have lowered them sufficiently to make use of them for any pur- 

 pose whatsoever. 



* Extract of a letter dated Philadelphia, March 23, 1802, a copy of which has 

 been kindly forwarded to me by Mr. EverarJ Home, 

 i" Historical Disquisition, page 52. 



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