TRITUBKRCULY IX PRLMATKS (55 



In the lower molar teeth the order of calcification is precisely 

 the order of evolution, in other words, the anterior buccal was 

 the first to evolve, representing the reptilian cone ; it is also the 

 first to calcify. The anterior lingual is the second in age, and also 

 the second to calcify. The third and the fourth cusps calcify almost 

 simultaneously. So we find that the order of embryonic development 

 exactly repeats the order of historical development, and in every way 

 presents the strongest kind of confirmation of the theory of cusp 

 formation which we have been discussing. But this you see is not 

 exactly the case in the upper molars. Nevertheless, out of eight 

 cusps in the upper and lower molars considered together, six cusps 

 calcify in the order in which they were successively added to the 

 single reptilian cone. 



Gentlemen, I trust that I have not in this address taken you 

 too far afield. I have reached a conclusion on this subject which 

 could be elaborated in much greater detail. In closing, I would 

 like to refer to the work of Dr. J. L. Wortman, who is here this 

 evening, and who was for some years a collaborator with Professor 

 Cope in Philadelphia, and who in association with Professor Cope 

 had quite a share in the establishment of the " tritubercular or cusp 

 addition " theory. This theory is now a rival to the " concrescence " 

 theory ; and, while it may not seem a matter of great importance, if the 

 concrescence theory may not seem one we ought to take seriously, still, 

 iu view of the attention which it has gained in Germany, it is 

 time that we produce and bring forward the unimpeachable evidence 

 which we get of the history of these teeth from the rocks, the solid 

 evidence from the geological formations, the evidence of comparative 

 anatomy, which, as we have just seen, is so far supported by the 

 evidence of embryonic development. 



BIBLIOGRAPHY. 



Works of reference in addition to those cited above : 



Rose, " Ueber die Entwickelung und Formabanderung der menschlichen Molaren," 

 Anatomisch&r A:<'i(/er, Band VII., 1892. 



Kukenthal, '' Ueber den Ursprung und die Entwickelung der Saugethier- 

 /iihne," Jenaische Zeitschrift fiir Naturwissenschaft, Band 28, 1893. 



Osborn, "The Evolution of Mammalian Molars to and from the Tritubercular 

 Type," American Naturalist, 1888, p. 1067. 



"The History and Homologies of the Human Molar Cusps," Anatomischer 

 Anzeiyi-r, VII., 1892, pp. 740-747. 



Cope, " The Mechanical Causes of the Development of the Hard Parts of the 

 Mammalia," Journal of Morphology, III., 1889. 



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