Animal Dentition 113 
much more numerous than in _ ordinary 
mammals; secondly, they are all alike; and, 
thirdly, they are in the form of simple 
cones. It might at first sight seem probable 
that dolphins present the primitive type of 
dentition from which the various more com- 
plicated forms have been evolved. But there 
are several reasons against this view, notably 
the fact that ancestral dolphins had teeth 
differentiated into the usual three series, and those of the cheek-series complex in 
structure. Possibly modern dolphin-teeth may have been produced by the splitting of 
earlier three-cusped teeth. Be this as it may, it is perfectly evident that dolphins have 
undergone a retrograde or degenerate dental development. Not that by this I mean 
to infer that their dentition is ill-adapted to their mode of life. Quite the contrary, 
for their numerous sharp-crowned teeth are well fitted to seize and break up the fish, 
cuttles, or squids on which these creatures subsist. One kind of dolphin—the Arctic 
narwhale—has an altogether peculiar type of dentition, the males being furnished with 
the well-known spiral tusk, which is usually developed only on the left side of the upper 
jaw, although in rare instances those of both sides attain full development. There has 
been much dispute as to the function of these splendid fluted tusks; but as the females 
manage to get on perfectly well without them, they are probably used as fighting- 
weapons by their owners. Of course there is the reply that if the males of other 
dolphins can conduct their battles without the aid of such weapons, the narwhale could 
do likewise. But objections of this nature could be raised against any theory of the 
function of these teeth that might be suggested. 
Taking leave of mammals whose diet is composed to a greater or less extent of 
flesh, we may turn our attention first to the omnivorous and then to some of the 
purely herbivorous forms. An excellent example of the former is afforded by the wild 
boar and other members of the pig tribe. Here it will be seen (Fig. 9) that large 
and powerful tusks are retained, and that the hinder molars have broad and flattened 
crowns (Fig. 10) surmounted by blunt tubercles. Their teeth, in fact, recall to a 
certain extent those of the bears. Uhe earlier molars, on the other hand, have 
laterally compressed and cutting crowns, well suited for breaking-up roots and tubers 
before they are subjected to the crushing action of the hinder teeth of the series. 
The forward inclination of the lower incisors is doubtless 
also an adaptation to the needs of an animal which obtains 
much of its food by grubbing in the ground. From those 
of the carnivora the tusks of the wild boar differ not only 
by the circumstance that the summits of the lower pair are 
worn against the sides of the upper ones so as to produce 
an oblique cutting-edge of razor-like keenness, 
but likewise by their peculiar semicircular 
curve and the fact that they continue to grow 
throughout the life of them owners. From 
this it results that when the upper tusk of a 
wild boar is broken off, the lower one continues 
to grow till it forms an almost complete circle 
and the tip pierces the jaw close to its point 
of origin. Advantage of this peculiarity is 
taken by the natives of New Guinea and 
Fig. 8. Side view of the Teeth of a Dolphin. 
Figs.9 and 10. Side view of Dentition of Wild Boar, and 0 2D 
Crown Surface of last left Upper Molar of same. elsewhere, who, by breaking off the upper 
