88 A COURSE ON ZOOLOGY. 



six below. Back of them, on each side, and above and 

 below, is a long conical canine, about three times the size 

 of the incisors. Still back of these are the large, thick, 

 and irregular molars, seven on each side below, and six 

 above, having great conical projections, somewhat pressed 

 together from the sides. 



Some of the molars have a single root, and are called 

 premolars ; these are in front of the true molars, which 

 have double roots. In the upper jaw there are three 

 premolars on each side, while there are four in the lower 

 jaw. 



The prominences that are noticeable on the crowns of 

 the true molars are ordinarily rounded ; however, the 

 anterior lower molar on each side is armed with several 

 sharp points, and hence is called the carnivorous tooth. 

 In the upper jaw the last premolar on each side is car- 

 nivorous. 



In the mammals the number and kind of teeth in the 

 jaws are expressed briefly by dental formulae. These 

 formulae are composed of the first letter of the name of 

 the kind of tooth, followed by a fraction whose numer- 

 ator is the figure expressing the number of teeth in the 

 upper jaw, while the denominator gives the number of 

 corresponding teeth in the lower jaw. The formulae are 

 still further simplified by expressing the teeth on only 

 one side of the face, and, as the teeth are always sym- 

 metrically arranged, double the number given by the 

 formulae will be the total number of teeth. Thus, the 

 formula for a dog's teeth is 



I f , C |, Pm f, M f . 



The sum of these numbers is 21 ; there are, therefore 

 twenty-one teeth on each side, or forty-two in all. 



