ELEPHANTS. 



525 



ing as high up in the skull as the aperture of the nasal cavity. In the young state 

 the tusks of the living species of elephants are tipped with enamel ; hut this is soon 

 rubbed off by use, and they then consist of ivory alone. This ivory differs from 

 that of other mammals in its structure, which renders it easy to distinguish 

 elephant-ivory from all other; and if a transverse section of a tusk be examined, it 

 will be found to present a pattern like the engine-turning on the back of a watch- 

 case ; this peculiar pattern being absolutely distinctive of true ivory. 



We come now to the consideration of the molar or cheek-teeth of the elephants, 

 which in their structure and mode of succession are unlike those of all other 

 mammals. In the first place, an elephant has six cheek-teeth on each side of both 

 the upper and lower jaws ; but instead of all these being in use at once, in the 

 existing species only two 

 are ever above the gums 

 at any one time, and one of 

 these is but partly pro- 

 truded; while in old animals 

 there is but a single tooth 

 remaining. The molar 

 teeth are elongated from 

 front to back, and are com- 

 posed of a number of trans- fci^Tl* 

 verse ridges closely packed 

 together. The anterior 

 teeth, as shown in the 

 accompanying figure, are 

 small, and include but few 



ridges ; but each succeeding tooth is larger, and comprises a greater number of ridges, 

 reaching in the last molar of the Indian species to as many as twenty-four. The 

 individual teeth succeed one another from before backwards in an arc of a circle ; 

 and as the tooth in front is worn away, its place is gradually taken by the one rising 

 from behind, till at length the sixth and last tooth alone remains. Although this 

 mode of succession appears strange and peculiar, it is in reality only an ultra-develop- 

 ment of what takes place among the pigs, and more especially in the African wart- 

 hogs. In all the pigs the last molar does not come into use till the teeth in front 

 of it are considerably worn ; and in the wart-hogs, as we have already seen, the 

 last molar is of unusually large size, and may be the only cheek-tooth remaining 

 in the adult condition, owing to those in front being shed. It should be added that 

 while the last three cheek-teeth of the elephants correspond to the true molars of 

 an ordinary mammal, the three anterior ones represent the last three milk -molars 

 of such an animal as the pig, and not, as would at first sight appear to be the case, 

 the premolars. That the three teeth in question are really milk-molars is proved 

 by the circumstance that in some of the extinct species they were vertically suc- 

 ceeded by teeth of simpler structure corresponding to the premolars of the pig. 



In order to understand the structure of the molar teeth of the elephants, it 

 will be advisable to take those of one of certain extinct species which, like Clift's 

 elephant, exhibit a simpler conformation than those of the existing species. Such 



THE FIKST AND SECOND RIGHT UPPER MOLAR TEETH OF THE 



mammoth (nat size). — After Sir R. Owen. 



