112 Animal Life 
the third tooth behind the tusk in the upper jaw and likewise the third in the lower 
jaw are the flesh-teeth. On the other hand, the molars to the rearward of the flesh- 
teeth (Figs. 5 and 6) are very large, and have broad crown-surfaces surmounted with 
small blunt tubercles. Apparently the teeth between the tusks and the flesh-teeth are 
of no use to a bear, for we find them very smal! and falling out at an early age. 
As a whole, the bear’s dentition is adapted to a diet of roots and fruits rather than 
to one of flesh; and we know that most of these animals feed chiefly on substances 
of the former nature, supplemented from time to time by a meal of carrion. From 
a certain resemblance between them it might be supposed that the molar teeth of 
bears and pigs are derived from a common ancestral type. Such, however, is not the 
case, since it has been ascertained that bears are the descendants of dog-like animals. 
Accordingly we may consider that their cheek-teeth have undergone a kind of retrograde 
or degenerate development. That is to say, the dentition, after being specialised up 
to a certain stage for purely carnivorous habits, subsequently underwent a further 
specialisation for habits of a precisely opposite nature. 
Although seals are as purely carnivorous as any animals, thei cheek-teeth are 
totally different from those of the land carnivora. Fig. 7 shows in profile the 
dentition of the leopard-seal of the Antarctic, in which the teeth attaim the extreme 
development of the structure charac- 
teristic of the true, or earless, seals 
in general. It will be seen that 
all the five pairs of cheek-teeth in 
each jaw are practically identical in 
character, and consist essentially of 
three sharp recurved conical cusps 
placed one before another; there is 
thus nothing to correspond with the 
flesh-teeth of the land carnivora. 
Such a type of dentition is obviously 
adapted to the retention of slippery 
prey lke fish, on which so many 
seals subsist. It 1s inferred from 
the absence of all trace of flesh- 
teeth that seals are not descended from any of the land carnivora as we now know 
them, but may trace thew ancestry direct to certain early forms which had not 
developed the characteristic flesh-teeth. The earless seals, or sea-bears and sea-lions, 
on the other hand display a different type of dentition; and it is far from improbable 
that these animals are more nearly related to the modern land carnivora, especially 
the bears. The walrus stands quite alone among the seals as regards dentition, having 
a pair of very long tusks in the upper jaw and a small number of simple flat-crowned 
teeth in both jaws. Here, again, we have an obvious instance of adaptation to habits, 
the long tusks being for raking up the mussels and clams on which the walrus feeds 
(and perhaps also at times to assist the animal in hauling up its bulky carcase on 
to land or ice), while the flat-crowned cheek-teeth are admirably suited to crushing their 
hard shells. Probably there is no mastication, the crushed bivalves being swallowed 
whole, like oysters. 
Quite unique among mammals is the type of dentition displayed by dolphins and 
grampuses and their gigantic relative the sperm-whale. In the former animals teeth 
are developed in both jaws, but in the sperm-whale they are confined to the lower 
jaw. There are three peculiarities in regard to the dentition of the “toothed whales,” as 
the foregoing species and their relatives ave termed. In the first place, the teeth are 
AW 
Vi 
Fig. 7. Side view of Dentition of Leopard-Seal. 
