DENTAL FOKMULA. 



57 



certain number of teeth, called the milk teeth, are shed 

 and replaced by others. But there are many kinds of 



FIG. 6-1. 



Molars. Pre-Molars. Canine. Incisors. 



Teeth of the left half of the lower jaw of the highest Mammal Man. 



mammals in which no such shedding and replacement 

 have been observed. 



And here it may be stated that it is common among zoologists to 

 indicate the kinds and number of teeth in any mammal, by a formula. 

 Thus the formula for the teeth of Man is : 



2-2 



1-1 



2-2 



which means that Man has two incisor teeth in each side of each jaw, 

 one canine tooth in each side of each jaw, two pre-molar teeth in each 

 side of each jaw, and three molar teeth in each side of each jaw, 

 making in all thirty-two teeth. 



Sometimes the dash ( ) is omitted as it obviously merely indicates 

 that the teeth of a given kind are equally arranged in the right and 

 left side of the mouth and then the formula is written thus : 



424 

 -. c _ pm ., 



4' 2' 4 



-=32. 



With these examples all similar formula} will be readily understood. 



In general the Mammalia have seven vertebra? in the 

 neck ; but there are some important exceptions. The Ma- 

 nati(seep. 114) have only six, one species of Sloth has only 

 six, and the Three-toed Sloths have nine! 



The first and second cervical vertebra? are articulated with each 

 other and with the two occipital coudyles (Fig. 63, oc), by gynovial 



3* 



