114 Animal Life 
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Fig. 11. ~~ = ¥ WL 
Figs. 11 and 12. Side view of the Dentition of the Giraffe, and Crown Surface of 
left Upper Molar of the same. 
mit 
tusks of wild boars kept in captivity, obtain without further 
trouble beautiful armlets formed by the overgrown lower tusks. 
Since the food of pigs requires comparatively little mastication, - 
molars with low crowns and of simple structure fulfil all 
requirements. Not so with the ruminants and other mammals 
which subsist on grass or leaves. These substances require an immense amount 
of mastication, and we consequently find that the molars of the ruminants (Fig. 12), 
instead of being surmounted by simple blunt tubercles, are crowned with four 
crescents separated from one another by deep pits, the crescents being turned in 
opposite directions in the upper and lower jaws. In the giraffe, which subsists by 
browsing, the crowns of the molars are not very much taller than in the pig, but in 
many antelopes and all sheep and oxen, which graze, these crowns become very tall, 
and thus take much longer to wear out than would otherwise be the case. From this 
it may be inferred that grass (and corn) takes a much greater amount of mastication 
than is necessary for leaves, and we may trace a gradual heightening of the molars 
as we pass from the browsing giraffe through the deer, which feed partly on leaves 
and partly on grass, to sheep and oxen, whose food is almost exclusively formed 
by grass. 
In groups which have not to procure for themselves animal food and do not 
depend upon their tusks to defend themselves from peril, it is obvious that there will 
be little or no use for these weapons. In the camel, indeed, which is of a spiteful 
and aggressive disposition and is in the habit of inflicting very nasty bites, tusks, 
although of reduced dimensions, are retained in both jaws. The true ruminants, on 
the other hand, such as the giraffe (Fig. 11), deer, antelopes, and oxen, have either 
completely lost their upper canines, or these are reduced to mere insignificant rudiments. 
Moreover, all these animals have entirely lost all their upper incisor teeth, which are 
replaced by a hard callous pad, against which the lower incisors bite. Looking at 
the figure of the lower jaw of the giraffe, the reader might well imagine that the 
ruminants had also lost thei lower canines. This, however, 1s not the case, these 
teeth having assumed much the same shape as the lower incisors, and with them 
forming a contmuous series of four pairs in the front of the lower jaw, separated by a 
long gap from the cheek series, and admirably adapted to twist off bunches of grass 
or leaves by nipping tightly against the hard pad in the front of the upper jaw. 
The giraffe’s dentition is, however, worth a moment’s further consideration. An 
inspection of the drawing will show that the crowns of the outermost of the four 
pairs of lower front teeth have bilobed crowns, whereas those of a deer or an antelope 
are simple. What is the meaning of this? Anyone who may watch a deer browsing 
will see that it eats both leaves and the smaller twigs on which they grow. A giraffe, 
Fig. 12. 
