3 oO PHYSIOLOGY AND MORPHOLOGY OF ANIMALS. 



This was probably the number in the early Tertiary 

 mammals ; any less number is the result of gradual abor- 

 tion. Thus ruminants have no front teeth in the upper 

 jaw, but the rudiments of these buried in the jawbone 

 unborn show that they came from animals having a full 

 set. The same is true, as already explained (page 260), 

 of whales, and also of edentates, etc. 



(c) Structure of Molars. — Molars are the masticatory 

 teeth, and are therefore, more than all others, subject 



to variation accord- 

 ing to the character 

 of the food. In this 

 regard there are three 

 main kinds, viz., om- 

 nivorous, carnivorous, 

 and herbivorous. Om- 

 nivorous molars are 

 simply tuberculated, 

 and are equally adapt- 

 ed to all kinds of 

 food, but not specially and perfectly adapted to any one 

 kind. Such are the teeth of man, of monkeys, of bears, 

 and the hog (Figs. 181, 182, 183). 



Fig. 181. — View of teeth of the right side 

 of the upper jaw of man. 



Fig. 182.— Teeth of the right side of the upper jaw of a monkey. 



Carnivorous molars are specially adapted for flesh 

 eating. They only crush and divide the food sufficiently 

 for swallowing, but do not grind or triturate it. This is 



