of the wild Boar, and Animal incognitum. 327 
of the lower jaw is totally unlike; and there are four grinding 
teeth on each side of the jaw, with flat crowns, on which are 
transverse grooves ; which shows that the number and appear- 
ance of the teeth are very different from those of the animal 
incognitum of North America. This South American animal 
incognitum, therefore, having no tusks, cannot be brought in 
evidence either for or against their existence in the other. 
The mode of dentition by a succession of large grinders 
formed in the posterior part of the jaw, is not the only one 
adopted by nature for the supply of those animals who live to a 
great age, and require a renewal of their teeth, with an increase 
of size proportioned to the enlarged growth of the animal. 
Crocodiles and seals live to a considerable age, and grow to a 
very large size ; but, from the nature of their food, their teeth 
are small ; and therefore, in those animals, the succession is 
from the portion of the jaw immediately under those which 
are to be shed. As the jaw becomes larger, the teeth increase 
in size, but never so much as to prevent there being room 
for the growth of the new tooth under the old, although the 
succeeding teeth are three or four times larger than the original 
ones, in both these genera of animals. 
The mode of dentition in the elephant, animal incognitum, 
and boar, appears to be confined to those animals of great 
longevity, whose food has so much resistance as to require 
the teeth being of a size too large to admit of the new tooth and 
the old being contained in the same portion of the jaw, at the 
same time. 
That the elephant lives to a great age, is sufficiently ascer- 
tained ; and the size of the bones of the animal incognitum, is 
almost sufficient evidence of its being a long lived animal. 
