8 AGE OF THE DOMESTIC ANIMALS. 



The teeth of both dentitions are placed in each jaw so as 

 to form more or less of an arch, or horseshoe, the convex por- 

 tion forward and the open end facing toward the posterior part 

 of the mouth and throat. These arches are subdivided into 

 three portions, an anterior, a lateral, and an intermediate, and 

 in each section the teeth have characters which distinguish them 

 from the others, and distinctive forms which indicate the use to 

 which they are adapted. 



In the anterior arcli the teeth are sharp-edged, and are 

 adapted for cutting or nipping the food ; these are called incisors 

 {incidere, to cut), and are most characteristic in the herbivora. 



In the intermediate section the teeth are large, pointed, 

 and sharp, destined to tear the food or to serve as weapons of 

 offense and defense ; these are called tusks, tushes, fangs, or 

 canine teeth ; they are most developed in the carnivora, which 

 tear their food. 



The lateral arches have broad, strong teeth, with flat sur- 

 faces, admirably fashioned for the grinding of the food, from 

 which they take the name of molars (molere, to grind), or 

 grinders. These are sometimes subdivided into 2^ ^'emol a rs and 

 post-molars, or molars proper. 



As the teeth on the two sides are symmetrical, for conveni- 

 ence of description zoologists have adopted the following formula 

 to indicate the number of teeth in either dentition or at any 

 given period of an animal's life ; it gives only the teeth on one 

 side of the mouth : — 



I = incisors, T r= tusks, M =r molars. 



Thus, for the permanent dentition of the horse : — 



Superior jaw ) j 3 .j^^ 1^ ^ 6 ^ _ ,0 ; both sides, 40. 

 Inferior jaw ) 3 l 6 



Or, more simply : — 



3.1.6 



= 40. 



3.1.6 



