DEVELOPMENT OF THE TEETH IN MAMMALIA 37 



Osborn, in reply to this criticism, says : ' The further we 

 go back among the ancestors of the Multituberculates and 

 Rodents, the less polybunic and more tritubercular they 

 appear.' He holds that the multituberculate tooth is of 

 tritubercular origin. 



Leche (14), Taeker (25), and Rose, from the study of 

 development in the embryo, agree in stating that in mar- 

 supials, ungulates, and man the first cusp to develop is the 

 paracone and not the protocone. M. F. Woodward (28) also 

 confirms this observation, and says that the paracone is 

 identical with the primitive dental germ, and the protocone 

 is an internal ledge growing out from its base, and con- 

 cludes that the paracone in upper molars corresponds to 

 the primitive reptilian cone. In the lower teeth, however, 

 the successional development corresponds with the order 

 of the cusps in the trigonid of the lower molar. 



Marett Tims (26), working on the embryology of the dog, 

 comes to similar conclusions considering its molar to con- 

 sist of a primary cone, the paracone, a secondary cone, the 

 metacone, and three cusps derived from the cingulum, 

 which he considers plays a very important part in the 

 development of the mammalian molar. 



Smith Woodward (29), speaking of primitive trituberculy, 

 says 'this at first sight brilliant generalization can only 

 be accepted as a convenient working hypothesis which 

 remains on its trial', and Gidley (8) concludes that 'no theory 

 involving an absolute uniformity of succession in the develop- 

 ment of complex molars will hold true for all groups of 

 animals '. He considers, however, that the nomenclature 

 proposed by Osborn is very convenient for description, and 

 saves much confusion which would be- brought about by 

 any change in the descriptive terms used. While there have 

 been a great many criticisms of the tritubercular theory, it 

 has been very ably and impartially stated by Osborn, who 

 acknowledges many difficulties in the acceptance of the 

 theory in its entirety. 



The most recent investigation of the evolution of the Boik's 

 mammalian molar is that by Professor Bolk of Amster- res ^ arches - 

 dam (3). In discussing the views of this author we have 

 to distinguish between the fusion of teeth in an antero- 



