The Teeth
next claim attention. According to the dentition of the dog by M. Girard and Linnæus, the following is the acknowledged formula:
The full-grown dog has usually 20 teeth in the upper, and 22 in the lower jaw, with two small supernumerary molars. All of them, with the exception of the tushes, are provided with a bony neck covered by the gums, and separating the body of the tooth from the root. The projecting portion of the teeth is more or less pointed, and disposed so as to tear and crush the food on which the dog lives. They are of a moderate size when compared with those of other animals, and are subject to little loss of substance compared with the teeth of the horse. In most of them, however, there is some alteration of form and substance, both in the incisors and the tushes; but this depends so much on the kind of food on which the animal lives, and the consequent use of the teeth, that the indication of the age, by the altered appearance of the mouth, is not to be depended upon after the animal is four or five years old. The incisor teeth are six in number in each jaw, and are placed opposite to each other. In the lower jaw, the pincers, or central teeth, are the largest and the strongest; the middle teeth are somewhat less; and the corner teeth the smallest and the weakest. In the upper jaw, however, the corner teeth are much larger than the middle ones; they are farther apart from their neighbours, and they terminate in a conical point curved somewhat inwards and backwards.
As long as the teeth of the full-grown dog are whole, and not injured by use, they have a healthy appearance, and their colour is beautifully white. The surface of the incisors presents, as in the ruminants, an interior and cutting edge, and a hollow or depression within. This edge or border is divided into three lobes, the largest and most projecting forming the summit or point of the tooth. The two lateral lobes have the appearance of notches cut on either side of the principal lobe; and the union of the three resembles the
fleur de lis
, which, however, is in the process of time effaced by the wearing out of the teeth. (Figs. 3 and 4.)
While the incisor teeth are young, they are flattened on their sides, and bent somewhat backwards, and there is a decided cavity, in which a pulpy substance is enclosed. This, however, is gradually contracted as the age of the dog increases.
M. F. Cuvier speaks of certain supernumerary teeth occasionally developed in each of the jaws. There is much irregularity accompanying them; and they have even been supposed to have extended to seven or eight in number.
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