DENTAL SYSTEM OF MAMMALIA. 259 



and conspicuous Aveapon in tlie male narwhal, wlience the 

 name of its genus, of monodon, meaning single tooth. In 

 another cetacean, the great bottle- nose or hj^peroodon, the 

 teeth are reduced in the adult to tAvo in number, whence 

 the specific name H. hidens, but they are confined to the 

 lower jaw. 



The elephant has never more than one entire molar, or 

 parts of two, in use on each side of the upper and lower 

 jaws; to which are added two tusks, more or less de- 

 veloped, in the upper jaw. 



Some rodents, as the Australian water-rats {Hydromys\ 

 have two grinders on each side of both jaws; which, 

 added to the four cutting-teeth in front, make twelve in 

 all ; the common number of teeth in this order is twenty, 

 but the hares and rabbits have twenty-eight each. 



The sloth has eighteen teeth. The number of teeth, 1 

 thirty-two, which characterizes man, the apes of the old * 

 world, and the true ruminants, is the average one of the \ 

 class mammalia ; but the typical number is forty -four. 



The examples of excessive number of teeth are pre- 

 sented in the order Bruta, by the priodont armadillo, 

 which has ninety-eight teeth; and in the cetaceous order 

 by the cachalot, which has upwards of sixty teeth, though 

 most of them are confined to the lower jaw; by the com- 

 mon porpoise, which has between eighty and ninety teeth; 

 by the Gangetic dolphin, which has one hundred and 

 twenty teeth; and by the true dolphins {delpMnus)^ which 

 have from one hundred to one hundred and ninety teeth, 

 yielding the maximum number in the class Mammalia. ^ 



Form. — Where the teeth are in excessive number, as 

 in the species above cited, they are small, equal, or sub- 

 equal, and usually of a simple conical form. 



In most other mammalia, particular teeth have" special 



