58 COMPARATIVE DENTAL. ANATOMY 



mammal by means of what is called the Dental 

 Formula. In this scheme the teeth are repre- 

 sented by numbers in the form of fractions, — 

 those of the upper jaw being the numerator and 

 those of the lower jaw the denominator. Thus 

 the dental formula of Man is, for the permanent 

 teeth, — 



reading that he has on each side of each jaw 2 in- 

 cisors, 1 canine, 2 premolars (or bicuspids), and 

 3 molars, — the initial letter of each class being 

 used for abbreviation. The teeth of mammals 

 may be expressed in the same way. The decidu- 

 ous teeth of Man have the formula, — 



i. H c. H m. H = 20, 



2-2 1-1 2-2 



there being no premolars or bicuspids in the de- 

 ciduous series. The formula of the Elephant is, — 



. i_i o-o 6-6 oa 

 i. — c. — m. — = 26, 



0-0 0-0 6-6 



or of the Eat,- 



<•£-!! = -• 



The teeth of all mammals may be expressed in the 

 same manner. 



Single teeth are described in this system as fol- 

 lows with reference to the upper or lower series: 

 thus the left upper central incisor is noted i| x , — 



