272 Journal of Travel and Natural History 



where the full complement of incisors is present, the most de- 

 veloped incisors are the outermost — I. i is the smallest, I. 2 

 next smallest, and I. 3 largest ; and if we carry the canines into the 

 inquiry the position is still stronger : and we imagine that we may 

 fairly on this point reckon the canines as outer incisors. Although 

 springing from another bone, their form and intimate structure 

 assimilates them with the incisors rather than the molars. Facts 

 would appear, therefore, rather to tend to the opposite conclusion 

 from that of the theory. It would seem reasonable that the incisor, 

 which is most largely developed in general, should be that which 

 would be preferably developed in the case of a diminution in the 

 number. But the position of the tusks in this nine-tusker shews that 

 both conclusions are erroneous. According to the theory the normal 

 tusk of the elephant is incisor i, but in the nine-tusker there is a 

 small tusk in front of the large tusk, and it must therefore be No. 



1, so that the normal tusk is incisor No. 2; and our supposed con- 

 trary position, that it should be No. 3, based on the outermost inci- 

 sor being generally the largest, is also shewn to be untenable, 

 because in the nine-tusker there is a small tooth behind the normal 

 tusk, which must be No. 3. The truth seems to be, that any 

 of the incisors may take special development as a specific character. 

 And in the case of the Mastodon, Elephant, and Deinotherium, we 

 think there is reason to hold that all three have been respectively 

 so developed in turn. It appears to us that the tusk of the Mas- 

 todon represent incisor No. i, that of the Elephant incisor No. 2, 

 and that of the Deinotherium incisor No. 3. 



We take the occurrence of a small tusk in front of and another 

 behind the normal tusk in the nine-tusker to be probatio probata^ 

 that the tusk of the Elephant is incisor No. 2. If that is settled 

 it breaks up the theoretical rule, and we have then only to go by 

 probabilities drawn from analogies and resemblances. 



Now, the very first of these probabilities, drawn from 

 analogy, is, that as the tusk of the Elephant is incisor No. 



2, so should the tusk of the Mastodon and the tusk of 

 the Deinothere. But that this cannot be the case is at once 

 shewn by the representative tusk of both the Mastodon and 

 Deinotherium being both present in the under jaw of our nine-tusker. 

 They cannot both be the second incisor; consequently, the 

 analogy from the developed tusk in the Elephant being incisor No. 2 

 falls to the ground. The special development is obviously not 

 the same in all three, and as the Mastodontoid tusk is the inner one, 



