XIII 



PHYLUM CHORDATA 



565 



first upper pre-molar is almost always without a milk predecessor. 

 The Pigs (Fig. 1192) are among the very few recent Mammalia 



FIG. 1192. Left lateral view of the dentition of *the Boar {Sits scrofa), the roots of the teeth 

 being exposed. (After Flower and Lydekker.) 



which possess what has been referred to as a typical dentition : the 

 formula of the completed dentition is 



.3143 



The incisors of the upper jaw are vertical, those of the lower 

 greatly inclined forwards. The canines are greatly developed, 

 especially in the male, and grow from persistent pulps ; both the 

 upper and lower are bent upwards and outwards and work 

 against one another in such a manner that the upper wears on its 

 anterior and external surface, the lower at the extremity of the 

 posterior. The pre-molars are compressed, with longitudinal 

 cutting edges, and the molars provided with numerous tubercles 

 or cusps arranged for the most part in transverse rows (bunodont 

 type). The formula of the milk dentition is 





In the typical Ruminants there are no teeth on the prernaxillaB, 

 the incisors of the lower jaw and the canines, which resemble them 

 in shape, biting against a thickened callous pad on the opposed 

 surface of the upper jaw, and the upper canines are also usually 

 absent ; there are three pre-molars and three molars in both upper 

 and lower series, all characterised by the presence of column-like 



