Ruijal Institution. 329 



does anchylosis of the- tooth with the jaw constitute a normal mode 

 of attachment. Each tooth has its particular 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 MammaUan 

 class, to the maxillary, premaxillary, and mandibular, or lower max- 

 illary 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 apparent only in the lower 

 maxillary bone, as in the Cachalot ; or be limited to the superior 

 and inferior maxillaries, and not present in the premaxillaries, as in 

 the true Ruminants and most Bruta. 



The teeth of the Mammalia usually consist of hard unvascular 

 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, Quadrumana, and terrestrial Caruivora ; 

 it is thicker in the Herbivora, especially in the complex grinders of 

 the Elephant ; and is thickest in the teeth of the Sloths, Megathe- 

 rioids, Dugong, Walrus, and Cachalot. Vertical folds of enamel and 

 cement penetrate the cro^^■n of the tooth in the Ruminants, and in 

 most Rodents and Pachyderms, characterizing by their various forms 

 the genera of the last two orders ; but these folds never converge 

 from equidistant points of the circumference of the crown towards its 

 centre. The teeth of the quadrupeds of the order Bruta {Edentata, 

 Cuv.) have no true enamel ; this is absent likewise in the molars of 

 the Dugong and the Cachalot. The tusks of the Narwhal, "Walrus, 

 Dinotherium, Mastodon, and Elephant, consist of modified dentine, 

 which in the last two great proboscidian animals is properly called 

 "ivorv," and is covered by cement. 



The Dolphins and Armadillos present little variety in the shape 

 of teeth in the sa.nie animal ; the teeth are often \qt\ numerous ; 

 and this sameness of form is characteristic of most of the monophyo- 

 donts. 



In almost all the other Mammalia, particular teeth have special 

 forms for special uses : thus, the front teeth, from being commonly 

 adapted to effect the first coarse division of the food, have been called 

 cutters or incisors ; and the hack teeth, which complete its comminu- 

 tion, grinders or molars ; large conical 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 canine teeth, from being well developed in the 

 Dog and other Carnivora, although they are given, likewise, to many 

 vegetable feeders for defence or combat : e.r/. Musk-deer. 



Molar teeth,- which are adapted for mastication, have either tuber- 

 culate, or transversely ridged, or flat summits, and usually are either 

 surromided by a ridge of enamel, or are traversed by similar ridges 

 arranged in various patterns. Certain molars in the Dugong, the 

 Mylodon, and the Zeuglodon, are so deeply indented laterally by 

 opposite longitudinal grooves, as to appear, when abraded, to be com- 

 posed of two cylindrical teeth cemented together, and the transverse 



