344 ANATOMY OF VERTEBRATES. 



of non-ruminant Artiodactyles, the Hog. The permanent dental 

 formula of the genus Sus is illustrated in fig. 273. 



The upper incisors decrease in size from the first, i 1, to the 

 third, i 3, receding from each other in the same degree ; the first 

 is relatively larger in the Sus larvatus than in the Sus scrqfa ; the 



273 



Dentition of Boar (Sus). 



basal line of the enamel is irregular ; that substance extends more 

 than an inch upon the outer side of the tooth, but only two or 

 three lines on the inner side. The lower incisors are long, sub- 

 compressed, nearly straight ; the second is rather larger than the 

 first ; the third is the smallest, as in the upper jaw. 



The upper canines, in the Wild Boar, fig. 273, c, curve forward, 

 outward, and upward ; their sockets inclining in the same direc- 

 tion, and being strengthened above by a ridge of bone, which is 

 extraordinarily developed in the Masked Boar of Africa. The 

 enamel covering the convex inferior side of this tusk is longi- 

 tudinally ribbed, but is not limited to that part ; a narrow strip 

 of the same hard substance is laid upon the anterior part, and 

 another upon the posterior concave angle forming the point of 

 the tusk, which is worn obliquely upwards from before, and 

 backwards from that point. In the Sow the canines are much 

 smaller than in the Boar. Castration arrests the development 

 of the tusks in the male. 



The teeth of the molar series progressively increase in size 

 from the first to the last. The first premolar, ib. p i, has a 

 simple, compressed, conical crown, thickest behind, and has two 

 fangs. The second, p 2, has a broader crown with a hind-lobe, 



