The teeth which the jaws carry vary in number, and even in appearance, according to species; it is useful to note their differences. In order to establish the nature of these latter more effectively, we will first recall the fact that in man the teeth, thirty-two in number, are equally distributed between the jaws, and are divided into incisors, canines, and molars, of which the arrangement is thus formulated:
5_m._ 1_c._ 2_i._ | 2_i._ 1_c._ 5_m._ --------------------+-------------------- = 32.[19] 5_m._ 1_c._ 2_i._ | 2_i._ 1_c._ 5_m._
[19] _I.e._, _i_, incisors; _c_, canines; _m_, molars.
We also note that the incisors are edged, the canines are pointed, and that the molars, cubical in shape, have their surface of contact provided with tubercles.
The teeth of the cat are thirty in number; they are thus arranged:
4_m._ 1_c._ 3_i._ | 3_i._ 1_c._ 4_m._ --------------------+-------------------- = 30. 3_m._ 1_c._ 3_i._ | 3_i._ 1_c._ 3_m._
6_m._ 1_c._ 3_i._ | 3_i._ 1_c._ 6_m._ --------------------+-------------------- = 42. 7_m._ 1_c._ 3_i._ | 3_i._ 1_c._ 7_m._
In these animals, the incisors, such as are not damaged by use, are furnished, on the free border of their crown, with three tubercles, of which one, the median, is more developed than those which are situated laterally. We denote these teeth, commencing with those nearest the median line, by the names _central incisors_ or _nippers_, _intermediate_ and _corner incisors_. The canines, or _fangs_, are long and conical; they are curved backwards and outwards. The upper canines, which are larger than those of the lower jaw, are separated from the most external of the incisors (_corner_) by an interval in which the canines of the lower jaw are received. The lower canines, on the other hand, are in contact with the neighbouring incisors, and are each separated from the first molar which succeeds them by a wider interval than that which is situated between the corresponding teeth in the upper jaw.
The molars differ essentially from the teeth of the same class in the human species. Their crown terminates in a cutting border bristling with sharp-pointed projections; this formation indicates that these teeth are principally designed for tearing. During the movement of raising the lower jaw, which is so energetic in the carnivora, they act, indeed, in the same manner as the two blades of a pair of scissors. The largest molars are: in the dog, the fourth of the upper jaw, and the fifth in the opposite one; in the cat, the third both above and below.