ERUPTION OF THE PERMANENT TEETH. 



189 



third and fourth premolars appear, followed a month later by 

 the second premolar. 



One and a Half Years. — At eighteen months the interme- 

 diate incisors of both jaws make their appearance, and simulta- 

 neously the eruption of the third molar (seventh) takes place. 



After Two Years. — After two years the incisor teeth become 

 used with great irregularity, according to the nature of the food ; 

 the tusks increase in length and give some approximation of 

 their age, but insufficiently to be accurate. 



TABLE OF DENTITION OF THE HOG. 



MILK DENTITION. 



SCHWARTZKOPFF. 



SiMONDS. 



The following explanation of the causes influencin< 



the 



variations in the dentition of the pig is given by SchwarfzkopfF : — 



