KVOU'TIOX OF THK PREMOLARS 



199 



paraconid of the true molars; and may, therefore, be considered as 

 more or less serially homologous with that molar element. 



As 'A fourth stayc (or in some cases as the third stage of development 

 the order of succession not being- constant) there appears a cuspule on 

 the inner side of the crown of the protoconid which corresponds in 

 position with the metaconid of the true molars of the tritubercular 



j 4 ,s 



FIG. 200. Fourth lower prcnaolars of Creodonts in various stages of complication. After Scott. 

 1. Tiicentes sultrigoaus. family Oxyolcenidse. 

 _'. i 'In nodon protogonoides, family Arctocyonidfe. 



3. Ckriacus stenops, family Oxyclsenidse. 



4. Chriacus sc/ilijxaei-iniius. 



5. Deltatherium fundaminis, family Hyjenodontidje, tuberculo-sectorial pattern nearly com- 

 pleted, with a high trigonid and low talonid. 



Ani2>/tit/i<'riittH type, and subsequently develops into an exactly analogous 

 form. (This is the deuteroconid of Scott's terminology.) 



As a fifth stage a cusp is sometimes added to the premolar crown 

 on the internal or lingual side of the hypoconid, occupying- the position 

 held by the entoconid in the true molars. (To this Scott gave the 

 name of ' tetartoconid,' regarding it as serially comparable with the 

 tetartocone of the upper premolars.) 



Kn;. -201. Premolar complication in C'nndylarthra (Phenacodontid;e). Fourth lower premolar 

 nf right side, internal aspect. 1 and ~1. Pi-<itiii/oii<nlin> /" ,>f<"'tts, showing incipient metaconid and 

 t:il. mid. o. Ev.protorjoni.n /ilicif' /, showing better developed metaconid and talonid, incipient 

 parat-onid. The tuberculo-sectorial pattern is thus nearly attained. After Scott. 



On the completion of these four stages, the premolar readies a condition 

 analogous to the ' tuberculo-sectorial ' stage of the molars, namely, with 

 an elevated fri</onid composed of the protoconid, paraconid and metaconid, 

 and with a depressed fn/u/m/ composed of the hypoconid and entoconid. 



The subsequent transformation of the fourth inferior premolar in 

 various type is shown in the preceding and accompanying figures 

 (Figs. 200, 201). 



