30 COMPARATIVE DENTAL ANATOMY 



entire animal kingdom. In no set of organs is 

 the invention of nature so varied or the capacity 

 for change so great as in the teeth. This varia- 

 tion is due to the modifying influences of the 

 qualities of the various substances employed by 

 animals for food, for the teeth and jaws are 

 adapted to the particular manner of reduction 

 that the food of each species requires. It is an 

 adaptation of tools to material, not of material 

 to tools. Therefore there has arisen, in response 

 to the demands of food selection, a great variety 

 of forms of teeth. 1 The different kinds of food 

 have dictated the different kinds of tooth forms. 

 The force that dictates the tooth form is still 

 a matter of some dispute. The older writers be- 

 lieved that the shape of the tooth was influenced 

 by the movement of the jaw and a study of fos- 

 sils seems to bear that out. However, a study 

 of the embryology and histology of the teeth and 

 jaw seems to indicate that the shape of the tooth 

 has been responsible for the shape of the jaw and 

 the shape of the temporo-mandibular articulation. 

 The development of the tooth precedes the de- 

 velopment and final shaping of the jaws. Thus 

 in the carnivorous animals we find a tooth which 

 is long and the cusps of which are sharp, the 

 movement of the mandible is vertical and the 



l Teeth which are suited to the particular food have enabled the animal 

 to live, but there may have been many animals of the past whose teeth did 

 not change and the animals perished. — Editor. 



