196 EVOLUTION OF MAMMALIAN MOLAR TEETH 



the molars, is complicated by the addition on the inner or lingual side 

 of the protocone of a second cusp, which has appropriately been called 

 the deuterocone [Sevrepo?, second ; KWI/O?, cone] by Scott. This bicuspid 

 stage, which is retained in the ' bicuspids ' of man and other primates, is 

 the starting point, and brings out clearly the important initial fact 

 that in the premolars the protoconc remains upon the outer or buccal side 



pr 



FIG. 196. Fourth upper premolar of Creodonts and Carnivores in various stages of evolution. 

 (Cf. Figs. 84-92.) After Scott, 



1. DeltatkeTium fundaminis, family Oxycteuid*. 



2. Sinopa tahitue, family Hyaenodontidae. (Cf. Fig. 89.) 



3. Cynodictis gracilis, family Canidae. 



4. Felis concolor, family Felidse. 



of. the crown, while in the molars (as 'we have tried to show above, 

 pp. 35, 217) it shifts to the inner or lingual side. From this it follows 

 that the deuterocone of the premolars has no exact serial homologue 

 in any of the cusps of the molars, although it becomes functionally 

 analogous to the protocone ; it follows, moreover, that all the cusps 

 which are subsequently added to the premolars are analogous, but not 

 serially homologous, to those in the molars (Fig. 196). 



The Second xtaae of premolar complication usually consists in the 

 addition of a second outer cusp, posterior to the protocone, which, as the 



third in the series, Scott has called the 

 fi'itocone [T^O/TO?, third] ; this in turn is 

 analogous in position and function with 

 the inetacone of the molars. This tri- 



FIG. 197. Second upper premolar of tubercular fn'raspid Or trigOllOCloilt pre- 

 P>-otornh,p t >,<s n-,<licolns, a lower Eocene ,-,-,,,1.-,,. crarro imifafpa VPW nlriQplv flip 

 Equid(cf. Fig. 160), showing the division HlOiai Stage imitates \61} C1OS61} 



4ritVconI^ in X7scTr'' prot coliei " tritubercular or trigonodont molar tooth, 



and frequently the tritubercular types of 



premolars display intermediate conules corresponding in position with 

 the proto- and meta-conules of the molars, but obviously not homologous 

 with them. The gradual development of this tritubercular premolar 

 stage is beautifully shown in series of teeth of JEuprotogonia and 

 Phenacodus, in which the tritocone may be seen in all stages of 

 development from its incipiency, and in which the more anterior 

 premolars are seen taking up the stages which have already been 



