224 EVOLUTION OF MAMMALIAN MOLAR TEETH 



represents but one of several ways in which the complex molars of 

 different groups may have been derived. 1 



" 5. That in the forms derived from the trituberculate type 

 of molar the order of succession of the cusps is not the same in all 

 groups, and apparently homologous elements are sometimes developed 

 from different sources. Hence it follows that no theory involving an 

 absolute uniformity of succession in the development of complex molars will 

 hold true for all groups of mammals. 



' In the foregoing pages I have restricted the use of Osborn's 

 tooth-cusp nomenclature for the reason that, in this particular discussion, 

 there are some cases in which it is not strictly applicable and might lead 

 to confusion. 



" On similar grounds Dr. Wortman 2 has expressed the opinion that all 

 attempts to establish a tooth-cusp nomenclature founded on supposed 

 homologies are ' foredoomed to failure ' and should be entirely abandoned 

 as 'useless and confusing.' I agree with the general sentiment expressed 

 (op. cit., p. 366) that, owing to the adoption of different plans in different 

 groups of mammals for increasing the complexity of their molars, no 

 terminology founded on the basis of cusp homologies can be made strictly 

 applicable to all the mammalia. I do not, however, consider this 

 sufficient ground for abandoning absolutely so convenient a system of 

 nomenclature as that proposed by Osborn. Granting that many of the 

 terms proposed are founded on mistaken homologies, it does not 

 necessarily follow that they need be in the least confusing, as suggested 

 by Wortman. For in any system used, in order to make that system of 

 greatest convenience and highest utility, the names once adopted should 

 be permanent and not subject to transfer or substitution on any ground 

 of changed conceptions of homologies or history, for the same reason that 

 generic and specific names are retained regardless of the fact that they 

 may have been given to denote some supposed affinity or characteristic 

 which may later have proved entirely erroneous. 



" Viewed from the nomenclature standpoint, therefore, the convenient 

 names proposed by Osborn have come to assume an individuality which 

 conveys a far more definite meaning than any purely descriptive terms, 

 be they of relative position or supposed homologies. Moreover, they 

 have the valuable advantages of clearness and brevity in description. 

 On these grounds, in the opinion of the present writer, and for the added 

 reason that great confusion would inevitably result from any change in a 

 terminology that has found its way into so many publications, Osborn's 

 nomenclature should be retained as originally proposed. Thus the term 



Somewhat similar conclusions have been reached from different reasoning by E. S. 

 Goodrich, M. Tims and others. 



*Amer. Journ. Science (4), Vol. 16, 1903, 265-368. 



