1 1 14 THE UNGULATES, OR HOOFED MAMMALS 



minute pair of milk-tusks, which are shed at a very early age. The permanent 

 tusks, which are nearly cylindrical in shape, and taper to their extremities, con- 

 tinue to grow throughout the life of their owners, and thus remain permanently 

 open at their bases, which are inclosed in sheaths of the premaxillary bones extend- 

 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; but 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 its 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 Mam- 

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

 tipper 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 protruded; while 

 in old animals there is but 

 a single tooth remaining. 

 The molar teeth are elon- 

 gated from front to back, and 

 are composed of a number 

 of transverse ridges closely 

 packed together. The an- 

 terior 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 backward in an 

 arc of a circle; and as the tooth fn 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 ultradevelopment 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 

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

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

 naming m the adult condition, owing to those in front being shed. It should be 

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

 ars of an ordinary Mammal, the three anterior ones represent the last three 

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



THE FIRST AND SECOND RIGHT UPPER MOLAR 

 TEETH OF THE MAMMOTH. 



(Natural size. ) 

 (After Sir R. Owen.) 



