MASTICATION'. 



261 



young teeth, as seen in Fig. 107, where the edge or border of the tooth 

 is divided into three lobes, of which the most prominent constitutes the 

 point of the tooth. Between three and four years the upper central 

 incisors are worn, and between four and five the whole give indications 

 of much use (Figs. 109 and 110). Beyond this age the teeth are very 

 uncertain. The bluntness and yellow color of the tusks and other 

 teeth offer the best signs of increasing age. 



Fig. 106.— Milk-Teeth in a Puppy 

 2 ok 3 Months Old. (Gamgee.) 



Fig. 107.— Dentition in a Year-Old Dog. 

 ( Gamgee. ) ' 



Fig. 109.— Dentition in Dog between 

 3 and 4 Years of Age. (Gamgee.) 



FIG. 110- 



-Dentition in Dog 4 or 5 Years of 

 Age. (Gamgee.) 



Dentition in the Pig. — The pig is born with eight teeth, which are 

 ftetal incisors and foetal tusks. At one month four incisors are cut, 

 besides three temporary molars on either side of each jaw. Two more 

 temporary incisors are added to each jaw at three months, and all the 

 milk-teeth are then in position. The jaws and teeth grow, and at six 

 months in most animals, but not in all, a small tooth comes up on either 

 side of the lower jaw, behind the temporary tusks, between them and the 

 molars, and in the upper jaw directly in front of the molars. These 

 teeth have been mistaken for tusks. The fourth molar in position 



