70 KVOLUTION OF MAMMALIAN MOLAR TKKTH 



crest of the lower molars is termed the metalophid because it is always 

 developed from the metaconid or metastyle, and protoconid, never from 

 the paraconid ; the posterior transverse crest of the lower molars is 

 termed the hypolophid, because it is mainly formed by the hypoconid and 

 entoconid, never from the metaconid or paraconid. The external crest 

 of the upper molars is composed of so many cusps that it requires a 

 distinct prefix, but is readily remembered as the ectoloph. So with the 

 peripheral cusps, one or more of which are developed in all Ungulates, 

 and are especially numerous in molars of the Equidse ; to these the 

 terminal -style is applied in lieu of the English term ' pillar ' proposed 

 by Huxley we can readily locate the parastyle as the antero-external 

 buttress which is developed near the paracone, the mesostyle as developed 

 on the outer wall between the paracone and nietacone. Similarly, in the 

 lower molars, we find in several lines of Ungulates, but again most 

 conspicuously in the Equidae, that the metaconid and entoconid are 

 reinforced by little cusps which grow up behind them (a, a and l>, b, 

 Eiitimeyer) ; these may be termed respectively the metastylid and 

 entostylid, while the pillar arising secondarily in the primitive position 

 of the paraconid may be termed the parastylid. 



The principles upon which this terminology is based are therefore 

 very simple. 



1. The termination -cone is given to the main primary or central 

 cusps, and -conule to all intermediate cusps. 



2. The termination -style is proposed for the peripheral cusps arising 

 mainly from the cingulum. 



3. The termination -loph is applied to the crests. 



4. The seven prefixes are based upon the succession and position 

 of the elements in the primitive evolution of the crown, viz. : proto-,para-, 

 meta-, hypo-, cnto-, ecto-, mcso-. The prefixes are first applied to the 

 cones ; then to the styles, according to their proximity to the cones ; 

 then to the crests, according to the cones which mainly compose them. 



5. Homologous and analogous elements in the upper and lower jaws 

 are given similar terms, but distinguished arbitrarily by the terminal -id. 



Upon the opposite page are given the terms formerly employed by 

 French, German, and English authors for the teeth of the Ungulates 

 before their common tritubercular origin had been discovered by Cope. 

 In his ' Enchainements du Monde Animal ' Professor Gaudry, as far back- 

 as 1878, worked out most clearly the homologies of the molar elements in 

 the Ungulates from the sexitubercular-quadritubercular stage onwards ; 

 the valuable earlier studies of Riitimeyer 1 are well known. But now that 

 the ungulate molar has been found to converge to the uuguiculate molar 

 type, and both are found to contain the same elements, and to spring from 



1 Beitrage zur Kenntniss der fossilen Pferde, Berlin, 1863. 



