OF THE CLASS MAMMALIA. 5 



Dental characters. — The Mammalia, like Beptilia and Fisces, 

 include a few genera and species that are devoid of teeth ; the 

 true ant-eaters (^Myrmecophaga^, the scaly ant-eaters or pangolins 

 (Manis), and the spiny monotrematous ant-eater (JEchidna), are 

 examples of strictly edentulous Mammals. The Ornithorhynchus 

 has horny teeth, and the whales {Balana and Balcenoptera) have 

 transitory embryonic calcified teeth, succeeded by whalebone sub- 

 stitutes in the upper jaw. The female Narwhal seems to be eden- 

 tulous, but has the germs of two tusks in the substance of the 

 upper jaw-bones ; one of these becomes developed into a large and 

 conspicuous weapon in the male Narwhal, whence the name of its 

 genus Monodon. 



The examples of excessive number of teeth are presented, 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 common Porpoise, which has between eighty 

 and ninety teeth : by the Grangetic Dolphin, which has one hundred 

 and twenty teeth ; and by the true Dolphins {Delphinus) , which 

 have from one hundred to one hundred and ninety teeth, yielding 

 the maximum number in the class Mammalia. 



When the teeth are in excessive number, as in the Armadillos 

 and Dolphins above cited, they are small, equal, or sub-equal, and 

 usually of a simple conical form. 



In most other mammals particular teeth have special forms for 

 special uses ; thus, the front teeth, from being commonly adapted 

 to efiect the first coarse division of the food, have been called 

 cutters or incisors ; and the back teeth, which complete its com- 

 minution, grinders or molars ; large conical pointed 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 canines, from being well 

 developed in the Dog and other Carnivora. 



It is peculiar to the class Mammalia to have teeth implanted in 

 sockets by two or more fangs ; but this can only happen to teeth 

 of limited growth, and generally characterizes the molars and pre- 

 molars : perpetually growing teeth require the base to be kept 

 simple and widely excavated for the persistent pulp. In no mam- 

 miferous animal does anchylosis of the tooth with the jaw consti- 

 tute a normal mode of attachment. Each tooth has its peculiar 

 socket, to which it firmly adheres by the close co-adaptation of 

 their opposed surfaces, and by the firm adhesion of the alveolar 



