STRUCTURE OF THE INCISORS. 21 



D. It becomes triangular and has three (3) borders, one 

 anterior and two lateral. The summit of the triangle looks 

 backward. (Sections 8 to 11.) 



E. Finally the table surface is flattened from side to side. 

 (Sections 12 to 16.) This last form cliaracterizes very old age, 

 and lasts for the life of the animal. 



Girard designated this form of the tooth as biangular. 

 Distinctive shape in the dental table is much more regular, and 

 gives a more reliable source of judging the age in the pincher 

 teeth than in the intermediate, and more so in the latter than in 

 the corner teeth. The same is true of the incisors of the upper 

 jaw, but it is rare that we examine the table of these as an aid 

 in judging age, except in old animals from sixteen years to 

 twenty and over. 



STRUCTURE OF THE INCISORS. 



The study of the structure of the incisors of permanent 

 dentition furnishes valuable indications for determining the age 

 of the horse. This study is an indispensable adjunct for the 

 complete appreciation of the descriptions which have preceded, 

 and will allow us to understand better the peculiarities of form 

 which we find on the table of the tooth in its changes from 

 year to year. 



If we take as a type an inferior incisor at the moment of its 

 first appearance in the body of the jaw-bone, we find that it com- 

 mences as a germ, which consists of a sack (germ-follicle) into 

 the interior of which protrude two papillae, — one superior, a, and 

 one inferior, h (Fig. 11), which look toward each other. 



The first, the germ of the enamel (a), is of a conical form, 

 and is placed in what will become the dental cup. 



The second, the germ of the ivory (Z>), depressed from in front 

 to behind, fills the cavity which hollows out the root of the 

 tooth. 



The surface of the first is destined to the formation of the 

 enamel of the tooth, which function it completes by the time 

 the tooth has appeared through the gum, when the papilla 

 disappears. 



