TEETH OF MONOPHYODOXTS. 273 



tubes ; such denticles are cemented together laterally,, ib. c, 

 slightly decreasing in diameter, and occasionally bifurcating as 

 they approach the grinding surface of the tooth. The substance 

 of the entire tooth thus resembles the teeth of the Myliobates and 

 ChimtBroids among fishes, rather than any in the Mammalian 

 class, in which it offers a transitional step from the horny dental 

 substitutes, above described, to the true teeth. 



The teeth of the Orycteropus, when rightly understood, offer, 

 however, no anomaly in their mode of formation. Each denticle 

 is developed according to the same laws, and by as simple a 

 matrix, as those larger teeth in other mammals which consist 

 only of dentine and cement. The dentine is formed by calcifica- 

 tion of the pulp, the cement by ossification of the capsule ; both 

 pulp and capsule continue to be reproduced at the bottom of the 

 alveolus, part passu with the attrition of the exposed crown ; and 

 the mode and time of growth being alike in each denticle, the 

 whole compound tooth is maintained thoughout the life of the 

 animal. The augmentation in the size of the whole tooth, during 

 the growth of the jaw, is effected by the development of new 

 denticles, and a slight increase of size in the old ones, at the base 

 of the growing tooth, which, in the progress of attrition and 

 growth, becomes its grinding surface. 



The teeth of the Armadillo-tribe are harder than those of other 

 species of Bruta, the unvascular dentine being present in greatest 

 proportion, and forming the main body of the tooth ; it includes a 

 small central axis of vascular dentine, and is surrounded by an 

 extremely thin coating of cement. The numerous teeth in Priodon 

 are of very small size and simple form, and are all referable to 

 the molar series. They vary in number from twenty-four to 

 twenty-six in each upper jaw, and from twenty-two to twenty-four 

 on each side of the lower jaw, amounting to from ninety-four to 

 one hundred in total number. The Armadillos of the sub-genus 

 Euphractus, TVagler, are distinguished by having the anterior 

 tooth, which is shaped like the succeeding molar, 214 



implanted in the premaxillary bone. The two 

 anterior teeth of the lower jaw being in advance 

 of the premaxillary tooth, are, with it, arbitrarily 

 held to be incisors. 



Some species of the extinct loricate genus, 

 Glyptodon, surpassed the Rhinoceros in size, crown of tooth of great 



v M. . . . extinct Armadillo 



and the dentition was more complicated, and (Giyptodon ciavipesi. 

 more adapted to a vegetable diet, than that of the small existing 

 Armadillos. The osteo-dentine, fig. 214, o, occupied a larger 



VOL. III. T 



