298 FORM. 



the back-teeth which complete its comminution, grinders or molars ; 

 large conical teeth, situated behind the incisors, and adapted by 

 being nearer the insertion of the biting-muscles to act with greater 

 force, are called holders, tearers, laniaries, or more commonly 

 canine teeth, from being well developed in the Dog and other Car- 

 nivora, although they are given, likewise, to many vegetable feeders, 

 for defence or combat. 



The names 'incisors,' 'laniaries,' 'molars,' are not, however, 

 always indicative of the shape of the crowns of the teeth which 

 occupy the relative positions above mentioned. In some Carnivora, 

 for example, the front teeth have broad tuberculate summits adapted 

 for nipping and bruising, while the principal back teeth are as 

 admirably shaped for cutting, and work upon each other like the 

 blades of shears. The front teeth in the Elephant project, from 

 the upper jaw, in the form and direction of long pointed horns ; 

 in the extinct Dinothere the lower incisors had a similar form 

 and development, but were bent down from the end of the 

 jaw. Hence, therefore, shape alone has been found insufficient to 

 characterize the analogous teeth in the Mammalia, and it has been 

 necessary to consider the position, and also the mode of succession 

 of the teeth, in order to their definition and classification. 



Comparative Anatomists, by common consent, now apply 

 the term ' incisor,' arbitrarily, to those teeth which are implanted 

 in the intermaxillary bones and in the corresponding part of 

 the lower jaw. When the tooth which succeeds the incisors, 

 or the first of the upper maxillary bone, is conical, pointed, 

 and longer than the rest, it is called a canine, as is also its 

 analogue in the lower jaw, which always passes in front of it 

 when the mouth is closed. Of the remaining teeth, those which 

 are shed and replaced vertically, or which have successors de- 

 scending into their place in the upper, and ascending in the lower 

 jaw, are called 'premolars,' or false molars, and in Human Anatomy 

 ' bicuspides' ; the remaining teeth, which are not displaced by verti- 

 cal successors, but which follow each other from behind forwards, 

 in both jaws, are called molars, or true molars. 



Naturalists have availed themselves of the degree of constancy 



