VER TEBRA TA. 287 



as modifications of a common type of "appendage." 



For the sake of brevity, a series of figures called a 



dental formula is used to indicate the number of 



different kinds of teeth possessed by an animal. The 



upper row of figures in the formula refers to the 



upper jaw, the lower row to the lower jaw. Thus the 



teeth of man are 32 in number ; there are present 



on either side in each jaw two incisors, one canine, 



two premolars, and three molars : this may be written, 



. 2—2 1—1 2—2 3—3 00 



1. , c. -, pm. , m. ^ = oi : or, 



2—2 1—1 ^ 2—2' 8-3 



more shortly, by writing the half only and omitting 



2 ] 2 3 . . 



the total, i. ~, c. -, pm. J^, m. ;- ; while if 

 2 1 2 3 



2 12 3 

 it is written more shortly still, ^ ' an upright 



ti 1. Z o 



stroke may be added between the figure which 



represents the premolars and that which represents 



2 12 

 the molars, thus : 



3 



^. The milk teeth of man 



2 1 2 

 would similarly be represented by the formula, 



i. ^^, c. j=j-, d. m. ^^ = 20, d. m. standing 



for deciduous molars. In referring to one kind of 



tooth only, the full formula must be used, to prevent 



2 2 



mistakes : thus the incisors of man are - — -, that is 



2 — A 



to say two for each side in each jaw ; while the 

 canines are , and so on. The incisors are the 



