Now comes the question, which of these teeth are premolars, and which molars? This is decided by finding which of them have their place occupied in the young kitten by its first set of back-teeth, the _deciduous_ or _milk molars_, and which, on the other hand, have no predecessors: those which replace the milk molars being the premolars of the adult, those which arise as altogether new teeth, and have no representatives in the young animal, molars. The examination of a young Cat shows that there are, behind the canines, in the upper jaw three, and in the lower two teeth; that is to say, one less on each side of each jaw than in the adult. As age advances these deciduous or milk molars all drop out, and are replaced by the permanent premolars, while behind the last milk molar of each jaw an entirely new tooth makes its appearance--the true or permanent molar. Thus it is seen that only the last tooth in each jaw is a molar, and that the carnassials are of different natures in the two jaws, the upper being the last (third) premolar, the lower the single molar. [Illustration: MILK TEETH OF LION, EXPOSED BY CUTTING AWAY THE OUTER PORTIONS OF BOTH JAWS. (_Natural size. From Owen, after Rousseau._) _d.i_, deciduous incisors; _d.c_, deciduous canines; _d.m.1_, _d.m.2_, _d.m.3_, deciduous molars. The remaining letters have the same significance as in the preceding figure.] We therefore write the premolars of the Cat (3-3)/(2-2), and the molars (1-1)/(1-1), so that the whole “dental formula” is as follows:--_i._, (3-3)/(3-3), _c._, (1-1)/(1-1), _p._, (3-3)/(2-2), _m._, (1-1)/(1-1) = 30. In the milk dentition, the number of incisors and canines is the same as in the adult, and, as we have just stated, the molars are absent, so that the formula is _di._, (3-3)/(3-3), _dc._, (1-1)/(1-1), _dm._, (3-3)/(2-2) = 26, _di_, _dc_, _dm_, standing for deciduous incisors, canines, and molars. The tongue in this family becomes an important adjunct to the teeth, almost losing its character as a delicate organ of taste. The little elevations or papillæ which beset the tongue in all animals--in ourselves for instance--are formed into strong horny spines set closely together like the teeth of a file, and, as may be seen any day at feeding-time at the Zoological Gardens, used to rasp the flesh from the bones as effectively as any file would do it. Most people must have noticed the different texture of a Cat’s and a Dog’s tongue. In the latter it is as smooth as in ourselves, in the former it has more of the texture of a piece of coarse sandpaper.