6 EVOLUTION OF MAMMALIAN MOLAR TEETH 



be known as the ' EMBRYOLOGICAL THEORY.' It is another instance of 

 the apparent conflict between palseontological and embryological evidence 

 as witnesses of the ancient order of development. The final verdict, 

 therefore, will be most interesting. Briefly, the embryologists, especially 

 Eose, Taeker, Kiikenthal, M. F. Woodward, Marett Tims, have shown 

 that in the upper molars the cusp which Cope and Osborn assert to 

 be the oldest, is, on the contrary, later in development than the paracone, 



Order of Cusp Development 



Ja I a ontology 



FIG. 1. Order of cusp development as attested by Embryology (fide Rose) (left-band 

 numerals) and by Paleontology (fide Osborn) (right-hand numerals). Typical (synthetic) 

 dentition of Man, from Selenka. (The paraconid is not represented in human molars. 

 See p. 59 and Fig. 38.) 



and therefore (?) not the oldest palseontologically. The oldest upper cusp, 

 according to the ' embryological theory,' is the antero-external cusp 

 (paracone), and this is homologous with the reptilian cone ; from this 

 there is a slowly evolving triangle in the upper molars . according to 

 the same authorities the reptilian cone is, however, central or apical 

 in the lower teeth, embryology quite 'agreeing with palaeontology. From 

 this it would follow that the only serial homologies which can properly 

 be established are those between the lower and upper reptilian cones. 

 The embryological theory, in brief, is to the effect that while in the 

 lower molars the central reptilian cone remained external and the two 



