FORM OF PERMANENT TEETH. INCISORS. 



781 



no bicuspids among the temporary teeth, but the eight deciduous molars are 

 succeeded by the eight bicuspids of the permanent set. The relative posi- 

 tion and arrangement of the different kinds of teeth in the jaws may be 

 expressed by the following formula, which also exhibits the relation between 

 the two sets in these respects : 



Temporary teeth 



Permanent teeth 



( Upper 

 Lower 



MO. CA. IN. CA. MO. 



21412 =10 

 . ^^_____ = 20 



21412 =10 



MO. BI. CA. IN. CA. BI. MO. 



Upper 321412 3 = 16 



= 32 



(Lower 321412 3 = 16 



Special Characters of the Permanent Teeth. The incisors, eight in number, 

 are the four front teeth in each jaw, and are so named from being adapted 

 for cutting or dividing the soft substances used as food. Their crowns are 

 chisel-shaped, and have a si arp horizontal cutting edge, which by continued 

 use is bevelled off behind in the upper teeth, but in the lower teeth is worn 

 down in front, where it comes into contact with the overlapping edges of the 

 upper teeth. Before being subjected to wear, the horizontal edge of each 

 incisor tooth is serrated or marked by three small prominent points. The 



Fig. 538. 



Fig. 538. INCISOR TEETH OP THE UPPER 

 AND LOWER JAWS. 



, front view of the upper and lower 

 middle incisors ; 6, front view of the upper 

 and lower lateral incisors ; c, lateral view 

 of the upper and lower middle incisors, 

 showing the chisel shape of the crown ; a 

 groove is seen marking slightly the fang 

 of the lower tooth ; d, the upper and 

 lower middle incisor teeth before they have 

 been worn, showing the three pointed pro- 

 jections of the cutting edge. 



anterior surface of the crown is 

 slightly convex, and the posterior 

 concave. The fang is long, single, 

 conical, and compressed at the sides, 

 where it sometimes though rarely 

 presents a slight longitudinal furrow. 



The lower incisor teeth are placed 

 vertically in the jaw, but the corre- 

 sponding upper teeth are directed 



obliquely forwards. The upper incisors are, on the whole, larger than the 

 lower ones. 



In the upper jaw the central incisors are larger than the lateral ; the 

 reverse is the case in the lower jaw, the central incisors being there the 

 smaller, and being, moreover, the smallest of all the incisor teeth. 



The canine teeth (cuspid ati), four in number, are placed one on each 

 side, above and below, next to the lateral incisors. They are larger and 

 stronger than the incisor teeth. The crown is thick and conical, convex in 

 front and hollowed behind, and may be compared to that of a large incisor 



