56 COMPAEATIVE DENTAL ANATOMY 



comes more exact. Some species are devoid of 

 teeth entirely, as in some Ant-eaters. Others 

 have but one tooth, as the Narwhal. A Dolphin 

 has but two; the Elephant has but two incisors, 

 and but four molars in use at one time. Some 

 rodents have but two incisors and four molars in 

 each jaw; the Sloths have but eighteen teeth; 

 Man, the old world Monkeys, and some other 

 Mammals have but thirty-two teeth, etc. 



The number increases in various families to an 

 excessive degree: thus some of the Armadillos 

 have nine ty- eight ; some Whales sixty; the com- 

 mon Porpoise eighty to ninety; the Gangetic 

 Dolphin one hundred and twenty, and the true 

 Dolphin one hundred to two hundred. 



While there is thus great variation in the num- 

 bers of teeth in the various classes of Vertebrates 

 and even among the members of the same genera 

 and families, there is a rule governing all which 

 renders their study intelligible. This is based on 

 a scientific classification and arrangement by 

 means of which all teeth and tooth forms can be 

 properly understood. 



Vertebrate teeth are classified into various di- 

 visions having references to their forms, position, 

 and functions. In the fishes and reptiles the teeth 

 are adapted mainly for seizing and tearing, and 

 consequently are undifferentiated as to position 

 and function. There is little variety in different 



