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. THE INDICATIONS OF AGE. The dog displays natural indications of age. The hair turns gray to a certain extent as in the human being. This commences about the eyes, and extends over the face, and weakens the sight; and, at ten years old, or earlier, in the majority of dogs, this can scarcely be mistaken. At fifteen or sixteen years the animal is becoming a nuisance, yet he has been known to linger on until he has reached his two-and-twentieth year. Among the diseases from which the dog suffers, there are few of more frequent occurrence than decayed teeth, especially in towns, or in the habitations of the higher classes of society: the carious teeth, in almost every case, becoming insufferably fetid, or so loose as to prevent mastication; or an immense accumulation of tartar growing round them. The course which the veterinary surgeon pursues is an exceedingly simple one. If any of the teeth are considerably loose, they must be removed. If there is any deposit of tartaric acid, it must be got rid of by means of the proper instruments, not very different from those which the human surgeon employs. The teeth must be perfectly cleaned, and every loose one taken away. Without this the dog will be an almost insufferable nuisance. The decayed and loose teeth being removed, chlorinated lime diluted with 15 or 20 times its bulk of water should be applied to the gums. By the use of this the ulcers will quickly heal; the fetor will be removed, and the deposition of the tartar prevented. Mr. Blaine first introduced the chlorinated lime for the accomplishment of these purposes.