MOLAR TEETH. 293 



have no posterior tables, constituting shell teeth ; rarely they are 

 absent in every tooth when we have a shell mouth. The incisor 

 milk teeth are whiter than the permanent ones, and have distinct 

 necks, the necks of the latter being imaginary. They are convex 

 and grooved posteriorly, and have their dentine stained. Almost 

 perpendicular to the axis of the head, in the young animal, the 

 incisors become more and more horizontal as the animal ages. 

 Permanent incisors are convex anteriorly, the lower incisors having 

 one, the superior two grooves down the centre of the body ; these 

 are filled with cementum, but are absent in old teeth. The 

 incisor teeth attain their greatest development in the elephant, 

 in which animal they project from the mouth as tusks, it may be 

 to an enormous extent. 



' CANINE TEETH. 



The tushes, tusks, or canine teeth, well developed in dogs and 

 other carnivora, are simple teeth, four in number, a pair above 

 and below. They rest in the interdental spaces, the lower being 

 nearer the incisors than the upper ones ; they are permanent ab 

 initio, and appear between the fourth and fifth year, sometimes 

 a year in advance. The crown is somewhat conical, the base being 

 at the gums. The external surface is convex, and marked by 

 several fine longitudinal lines ; the internal surface presents on 

 either side a sharp ridge which separates it from the external. 

 The crown terminates in a conical eminence, somewhat hollowed 

 internally during growth, and bounded by a sharp ridge. When 

 a tusk has been long in wear, the ridge disappears, and the 

 internal surface becomes nearly smooth, and as the apex of the 

 tooth becomes worn away, often a small mark appears, but no 

 second ring of enamel. These teeth have no constricted neck, 

 and the fang is single. In the horse tribe, as a rule, canine teeth 

 are developed only in the male ; if they exist in the female they 

 are rudimentary. 



MOLAH TEETH. 



The Molars, or grinders, are 12 in the temporary set, 3 on 

 either side of each jaw ; 24 in the permanent set, 6 on each side 

 above and below; they are numbered from before backwards, 

 and like the incisors, those of the upper jaw are the larger. 



A molar tooth is constructed on the same general plan as an 



