15 



muscles, to act with greater force, are called holders, tearers, 

 laniaries, or more commonly canines, (ib. c,) from being well 

 developed in the Dog and other Carnivora. 



It is peculiar to the class Mammalia to have teeth im- 

 planted in sockets by two or more fangs ; but this can only 

 happen to teeth of limited growth, and generally characterizes 

 the molars and premolars : perpetually growing teeth require 

 the base to be kept simple and widely excavated for the per- 

 sistent pulp. In no mammiferous animal does anchylosis of 

 the tooth with the jaw constitute 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 periosteum to the organized 

 cement which invests the fang or fangs of the tooth. 



True teeth implanted in sockets are confined, in the Mam- 

 malian class, to the maxillary, premaxillary, and mandibular 

 or lower maxillary bones, and form a single row in each. 

 They may project only from the premaxillary bones, as in the 

 Narwhal ; or only from the lower maxillary bone, as in 

 Ziphius; or be limited to the superior and inferior maxillaries 

 and not present in the premaxillaries, as in the true Bumi- 

 nantia and most Bruta (Sloths, Armadillos, Orycteropes). In 

 most Mammals teeth are situated in all the bones above men- 

 tioned. 



The teeth of the Mammalia usually consist of hard un- 

 vascular dentine, defended at the crown by an investment of 

 enamel, and everywhere surrounded by a coat of cement. 



The coronal cement is of extreme tenuity in Man, Quad- 

 rumana and the terrestrial Carnivora; it is thicker in the 

 Herbivora, especially in the complex grinders of the Ele- 

 phant. 



Vertical folds of enamel and cement penetrate the crown 

 of the tooth in the ruminating and many other Ungulata, and 

 in most Eodents, characterizing by their various forms the 

 genera of those orders. 



No Mammal has more than two sets of teeth. In some 



