LIFE IN TERTIARY TIMES 303 



contour outline the base of the primitive tubercles. The 

 tuberculate teeth of the Rhinoceros have a flattened crown 

 but an elongated body, and thus evolved, as Boule has pointed 

 out, into the smooth, elongated teeth of Elasmotherium. In 

 Rodents we can follow all the transitions between the bossed 

 teeth of the Marmot and the rasp-like teeth of the Cabiai, 

 Beavers, Dormice, etc. The omnivorous cleft-footed 

 Mammals, of which our Wild Boar is typical, have retained 

 the mamillated teeth of Anthyacotherium, and Waldemar 

 Kowalevsky has created for them the sub-order Bunodontia. 

 These teeth are replaced in the herbivorous forms, which he 

 called Selenodontia, by teeth with a flat crown, formed by 

 juxtaposed crescents which represent the bases of the worn-down 

 tubercles of the Bunodontia. But as attrition always causes 

 the disappearance of the enamel on the surface of the teeth, 

 and as enamel is produced here in the ordinary way, it is 

 evident that there is no question here of inherited attrition. 

 In reality the dental germ takes the form determined by the 

 pressure transmitted to it, according to the use the animal 

 makes of its teeth while they are growing. Constant pressure 

 of upper and lower teeth one against the other must bring 

 about a flattening of the surface of the dental germ, and, as a 

 result, must cause it to produce a flat tooth which looks like 

 a worn tooth, with its tubercles reduced down to their bases, 

 these also looking like worn tubercles. The same obtains for 

 the lateral compressions in the teeth of Carnivora. 



The influence of the increasing development of certain teeth 

 on neighbouring teeth, already pointed out in connexion with 

 incisors and canines, is again encountered in the molars of the 

 Carnivora. Here the molars that do the most work are those 

 situated in the neighbourhood of the attachment of the 

 masticatory muscles to the jaw. They grow and develop that 

 cutting edge which has earned them the distinctive name 

 of camassials. They are already clearly characterized 

 in Dogs, some of which still have forty-four teeth. In the 

 Carnivorous group the other molars decrease in the front as 

 well as at the back of the carnassial teeth, and finally dis- 

 appear one by one in measure as we pass from the Dog to the 

 Civet, Marten, and Cat families. Thus their number decreases 

 from seven to two (Machcerodus). 



The reduction of the number of teeth is due, however, 



