1896.] MAMMLiLIiW DENTITION-. 589 



or metacone are as yet visible, while in Chrysochlork (fig. 36. 7) the 

 first indication of the protocone has appeared, viz. the internal shelf. 



This attempt to homologi/.e the main cone of the upper molars 

 of the Gentetidw and Ghrysocldoris with the paracone of other 

 Insectivora is a moditication of the view put forward by Mivart in 

 1868 (12). He regarded the tricuspid triangular crown of the 

 molar teeth of Centetes as a concentration of the eight cusped teeth 

 of Talpa. An examination of his figures and description will show 

 that he believed theao-called paracone and metacone of Centetes and 

 Chrysocliloris to be external cingulum cusps, the main cone of these 

 teeth being formed by a fusion of cones corresponding to the para- 

 and metacones of Talpa, while the protocone and hypocorie of the 

 latter he regards as represented by the small internal lobe seen in 

 ChrysoMoris '. This view accords in its most important respects 

 with mine, but I do not think that the ontogeny of the tritubercu- 

 late insectivore molar justifies Mivart's fusion theory, but rather 

 suggests that this tooth corresponds only with the paracone 

 triangle of the Mole's tooth. 



Such an hiterpretation would bring these forms into entire accord 

 with the other Insectivores and the Mammalia in general, and we 

 should then find that the cusp which directly continues the dental 

 germ, and consequently is the first to develop, is in all cases homo- 

 logous, though unfortunately the same name has not been applied 

 to it in all cases. 



Thus the primitive cone of the upper cheek-teeth of the ancestral 

 mammal finds its homologue in the protocone of the premolar, in 

 the paracone of most molnrs, but in the protocoue of the molars of 

 the trituberculate Insectivores and Pemlestes. This has been proved 

 ontogeneticaliy for both the premolars and molars, phylogenetically 

 also in the former, while in the latter the phylogeny of the 

 primitive cusp is still doubtful. 



The evolution of the primary cusp of the premolars and molars 

 is now brought into harmony, and it is no longer necessary to 

 suppose that the cusp arrangement of two teeth such as pni. 4 and 

 m. 1, often identical in pattern, have evolved upon difierent lines. 



To briefly recapitulate my conclusions : — 



(1) The antero-external eone, or paracone above and proto- 



conid below, is the primitive cone both in the molars and 

 premolars. 



(2) The protocone is borne on an internal shelf of secondary 



origin (internal cingulum). 



(3) The metacone is a similar backward development of the 



paracone, arising very early long before the protocone. 



(4) The hypocone stands related to the metacone as the 



protocone does to the paracone. 



(5) The paracone as the primary cone in the upper molars 



finds its homologue in the protoconid below ^. 



' Unfortunately the cones ha^e been incorrectly lettered in his figure of the 

 upper molar of Chrysochloris, as may he seen on reference to his description. 



'^ A paper by Winge (26) in Danish evidently upholds the same Tiew, viz., 

 that the paracone is the homologue of the protoconid ; unfortunately I am 

 unable to read the paper, but his lettering in his plate and diagrams are very 

 clear on this point. 



