14 



closer network than in Birds. The microscopic radiating 

 cells are relatively smaller and approach more nearly to the 

 spheroid form. 



The Mammalia, like Eeptilia and Pisces, include a few 

 genera and species that are devoid of teeth ; the true ant- 

 eaters (Myrmecophaga), the scaly anteaters or pangolins 

 .(Mam's), and the spiny monotrematous anteater (Echidna), 

 are examples of strictly edentulous Mammals. The Orni- 

 thorhynchus has horny teeth, and the whales (Balcena and 

 Balcenoptera) have transitory embryonic calcified teeth, suc- 

 ceeded by whalebone substitutes in the upper jaw. The 

 female Narwhal seems to be edentulous, 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 Cacha- 

 lot, 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 Gangetic Dol- 

 phin, 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 Arma- 

 dillos 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, (figs. 2 and 3, ,) from 

 being commonly adapted to effect the first coarse division of 

 the food, have been called cutters or incisors; and the back 

 teeth, (ib. m,) which complete its comminution, grinders or 

 molars; large conical pointed teeth situated behind the in- 

 cisors, and adapted, by being nearer the insertion of the biting 



