418 DR. C. I. FORSYTU MAJOR OX DENTAL [Mar. 15, 



approximately of the same size ; the premolar, however, is 

 slightly larger ; a further feature being that, having come in 

 place after m. 1 and m. 2, it is less worn than these two. 



By the criteria just mentioned, it is possible to determine the 

 anterior tooth in our specimen as the unique premolar, the three 

 teeth following as the three true molars. So that it is the fifth 

 tooth, the last in the series, which is supernumerary. It is 

 distinguished from all the others by its much smaller size, and by 

 reproducing only part of the pattern common to the anterior 

 teeth. Length of the four anterior molars = 35 millim., length of 

 the supernumerary = 4 millim. 



We have been told more than once that there are no individual 

 homologies in Mammalian teeth ; the reason, which apparently is 

 considered as the most weighty, being that " on the analogy of 

 what may be seen in the case of Meristic Series having a wholly 

 indefinite number of members, it is likely that the attempt thus 

 to attribute individuality to members of series having normally 

 a definite number of members should not be made." * 



The " definite number " is just what makes all the difierence ; 

 now that order, diSerentiation, division of labour have been esta- 

 blished, as the gradual outcome of what before had been chaos, at 

 least for our short-sighted eyes, we can begin to speak of individual 

 homologies, while before we could speak only of collective homo- 

 logies. And it is precisely the variations that help us towards 

 making out the individual homologies : witness E. Rosenberg's 

 researches on the variations occurring among the permanent 

 incisors of man t. 



The old truth that there is a common bond between all the 

 teeth of one specimen, does not invalidate their individuality. 

 They are all brothers, being children of one mother, the dental 

 lamina ; some slight peculiarity in the enamel pattern, by which 

 different species may be distinguished from each other, is often 

 enough common to all or to several of the cheek-teeth of one 

 specimen. In this connection an interesting fact, pointed out by 

 Bateson, is worth mentioning. When a supernvxmerary tooth is 

 added to the posterior end of the series, the normally ultimate 

 tooth, which has become the penultimate, is not unfrequently 

 abnormally enlarged. This circumstance is considei-ed by the 

 writer to favovir his view of the non-existence of individuality, 

 for "the new member of the series seems, as it were, to have been 

 reckoned for before the division of the series into parts." % To 

 me the obvious explanation appears to be, that by the increased 

 activity of the dental lamina, which not unfrequently takes place 

 at the end of the teeth-series, and results in the production of a 

 superntimerary tooth, the normally last tooth has profited as well ; 

 so that, as in so many other cases, the variation, the exception, 

 confirms the rule. 



* W. Bateson, ' Materials for the Study of Variation,' p. 273 (1894). 

 t Morph. Jalirb. vol. xxii. pp. 264-338 (1895). 

 X Proc. Zool. Soc. London, 1892, p. 111. 



