HOMOLOGIES OF THE TEETH. 809 



In the mammalian orders with two sets of teeth, these 

 organs acquire fixed individual characters, receive special 

 denominations, and can be determined from species to 

 species. This individualization of the teeth is eminently 

 significative of the high grade of organization of the ani- 

 mals manifesting it. Originally, indeed, the name "in- 

 cisors," "laniaries," or "canines," and "molars" were given 

 to the teeth, in man and certain mammals, as in reptiles, 

 in reference merely to the shape and offices so indicated ; 

 but they are now used as arbitrary signs, in a more fixed 

 and determinate sense. In some carnivora, e. g. the frftnt 

 teeth have broad tuberculate summits, adapted for nip- 

 ping and bruising, while the principal back teeth are 

 shaped for cutting, and work upon each other like the 

 blades of scissors. The front teeth in the elephant pro- 

 ject from the upper jaw, in the form, size, and direction 

 of long-pointed horns. In short, shape and size are the 

 least constant of dental characters in the mammalia; and 

 the homologous teeth are determined, like other parts, by 

 their relative position, by their connections, and by their 

 development. 



Those teeth which are implanted in the premaxillary 

 bones, and in the corresponding part of the lower jaw, are 

 called "incisors," whatever be their shape or size. The 

 tooth in the maxillary bone, which is situated at, or near 

 to, the suture with the premaxillary, is the " canine," as is 

 also that tooth in the lower jaw which, in opposing it, 

 passes in front of its crown when the mouth is closed. 

 The other teeth of the first set are the "deciduous molars ;" 

 the teeth which displace and succeed them vertically are 

 the "premolars;" the more posterior teeth, which are not 

 displaced by vertical successors, are the " molars" properly 

 so called. 



