ORDINAL TYI'KS OF MOLARS: TXCl'LATA 163 



Eii Ungulata. 



S !'!:< 7 A L REFEllEX<'l-:s. 



Dealing with the teeth of Ungulates from the tritubi-ri'tifur *tn adjoint. 



Schlosser, M., "Beitrage zur Keinitniss der Starnmesgeschichte der Hufthiere uiul 

 \Vrsuch einer Systematik der Paar- und Unpaarhufer," Mor/ilml. ././////>., 12, Taf. V., 

 VI. (see especially the " Allegemeiner Theil. Das Gebiss der Perissodaetylen und 

 Artiodactylen und seine Beziehungen zu dem der Condylarthra." pp. 97-112). 



"Die Differenzierung des Saugetiergebisses," BioL Centr<dl>L, Bd. X., Nr. 8, 1890 

 (especially pp. 247-250). 



Osborn, H. F., Antea, pp. 



FIGURE 135. 



No. 1. " Sexitubercular " superior and " quinquetubercular " inferior molar of Hyra- 

 cotherium (Eocene ancestor of the Horse), showing in the upper molar six 

 main cusps, a parastyle developing from the cingulum, and an encircling 

 cingnlum, continuous in the lower molar with the hypoconulid. The para- 

 conid of the lower molar is vestigial or wanting. The crown is low 

 (" brachyodont ") with low, conic cusps (" bunodont "). 



2. Superior molars of Pantolambda (Eocene Aniblypod). The triangular pattern 

 of the crown has been retained, the protocone remaining central in posi- 

 tion ; the outer cusps have become crescentic (" selenoid "), the parastyle 

 (ps) is extremely large (Fig. 140). 



3. Three stages in the degeneration of the paraconid seen in the lower molars of 



Amblypoda (Fig. 144). 



4. Superior and inferior molars of A. Systemodon (Eocene tapiroid) and B. 



Tapirus. The parastyle is seen developing from the cingulum, the inter- 

 mediates (pi., ml.) are conspiring with the outer and inner cusps to form 

 the "ectoloph," "protoloph," and "metaloph" (cf. 8) of the modern Tapir 

 (B). In the lower molars the paraconid is vestigial or absent. 



n. " Lophodont" type. Primitive Rhocerotoid molar (Hyrachyus) showing com- 

 pleted "protoloph," "metaloph," "ectoloph." 



6. " Lophodont " type. Modern Rhinoceros molar showing accessory folds, 



" antecrochet," " crista," " crochet." 



7. " Bunoselenodont " type. Primitive Titanothere (Palizosyops) . Internal 



cusps "bunoid," external "selenoid." 



8. " Lophoselenodont" type. Primitive (Eocene) Horse, Eohippus. Traces of 



the original triangular pattern of the crown are still discernible. 



9. "Lophoselenodont type." Primitive Horse (Packynolophus). The "inter- 



mediate connles" (pi., ml.) will become crenulate and with the ectoloph, 

 and the hypostyle, will produce the complex crown pattern of the modern 

 Horse. 



10. J. Upper molar of Ai_-li />/"///'//*, B. Lower molar of Merychippus, Miocene 



horses (cf. Fig. 160). 



11. " Selenodont " Artiodactyl type (Protoceras). All cusps crescentic. 



12. Ground plan of molars in various Ungulate sub-orders. A. Condylarthra (!) 



(Meniscot/terium), B. Amblypoda (Periptychus), C. Perissodat-tyla (Hyraco- 

 therium), D. Condylarthra (Phenacodus). 



