548 



ZOOLOGY 



SECT. 



The Pigs (Fig. 1204) are among the very few recent Mammalia 

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

 formula of the completed dentition is 

 .31 4 3 



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 up- 

 wards and out- 

 wards 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 sur- 

 face. The pre- 



FiG.;1204. Left iateral-viewof the dentition of the Boar (Susscrofa\ r^nla ar p nnm 

 the roots of the teeth being exposed. (After Flower ;and Lydekker.) 



pressed, with 



longitudinal cutting edges, and the molars are provided with 

 numerous tubercles or cusps arranged for the most part in 

 transverse rows (bunodont type). The first permanent pre-molar 

 has no predecessor, the formula of the milk dentition being 



.31 3 



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

 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 

 vertical folds of enamel, the interstices between which may be 

 filled up with cement the worn surface of the tooth presenting 

 a pattern of the selenodont type (Fig. 1193, V). In the Camels 

 there are a pair of upper incisors and a pair of large canines in 

 each jaw. 



