PART III. 



DENTAL SYSTEM OF MAMMALS. 



CHAPTER I. 



GENERAL CHARACTERS OF THE TEETH OF MAMMALS. 



124. The class Mammalia, like that of Pisces and Reptilia, 

 includes a few species which are entirely devoid of teeth ; these are 

 the Ant-eaters, forming, when clothed with hair, the genus Myrme- 

 cophaga ; when defended by scales, the genus Manis ; and when 

 armed with spines, the genus Echidna. A few Mammals have the 

 jaws provided with horny substitutes for teeth, as the Y\^halebone- 

 whales {Balcena and Balcenoptera) , and the Ornithorhynchus ; in 

 the rest of the class true teeth are present. In the Feline tribe 

 the epithelium of the tongue is thickened at the fore-part of its 

 dorsum, and invests the papill8e there with hard sheaths, like 

 prickles, which are analogous to the lingual teeth of certain Fishes 

 and Batrachians. The back part of the dorsum of the tongue in the 

 Echidna is provided with a plate of horny denticles, which bruise 

 its food against the hard and prickly epithelium covering the palate. 

 Horny processes, analogous to the palatal teeth of Fishes and Rep- 

 tiles, are likewise developed upon the roof of the mouth of the great 

 Bottle-nose Dolphin, thence termed Hyperoodon by Lacepede. 



125. Number. — In the last-named Cetacean, the true teeth are 

 two in number, whence its specific name, bidens : the Narwhal 

 likewise has but two teeth, both of which are concealed in the sub- 

 stance of the jaws in the female, whilst only one is ordinarily visible 

 in the male : but this grows to an unusual length. The Delphinus 

 griseus has five teeth on each side of the lower jaw ; but they soon 

 become reduced to two on each side. Amongst the Marsupial 



