288 THE DENTAL SYSTEM OF THE PRIMATES [SECT. A 



as trigonal and of lower molars as tuberculo-sectorial is really and 

 actually a more precise account than Cope 1 himself gave of the 

 molar teeth of the Puerco mammals upon which he originally 

 founded his theory. (Cf. Fig. 203.) 



The most recent modifications of the Tritubercular theory 

 having been reviewed, we may now enquire how far it applies to 

 the teeth of the Primates. 



The Lemurs present no difficulty at all as regards the upper 

 molar teeth for these are clearly tricuspid or tritubercular (cf. 

 Fig. 161). Tarsius shews the same form (Fig. 163). In the 

 Anthropoidea four cusps are found ; the original triangle has 

 thus an accessory cusp. Comparisons of various types and study 

 of the variations in the individual teeth shew that the additional 

 cusp is the postero-internal one, which as mentioned above 

 (p. 244, footnote) is termed hypocone 2 . The human upper molar 

 teeth resemble closely those of the other Primates in this respect 

 (Fig. 207). 



The lower molars are not so easily explained. In the Lemur- 

 oidea (Fig. 162) the first of these bears five cusps which we meet 

 again in the higher Primates. Tarsius retains the primitive form 

 (cf. Figs. 164 and 203 b). In the human lower molars, we find 

 the cusps disposed as shewn (Fig. 207). Reference to extinct 

 forms shews that the " original " lower triangle or trigonid has 

 lost a cusp, called the paraoonid 3 . The other diagrams in Fig. 207 

 shew the different parts of the original trigonid and also those of 

 the talonid or heel. The latter bears three cusps marked respec- 

 tively HYD, HLD, and ENT. D (the Hypoconid. Hypoconulid 

 and Entoconid of Osborn), though one of these, viz. the Hypo- 

 conulid (HL) is often wanting. These three cusps constitute the 

 " talonid." 



1 Evolution of Mammalian Molar Teeth, p. 2. 



2 It is convenient to note here that the four-cusped arrangement seen in the 

 upper molars of the higher Primates, was regarded by Cope as representing a 

 comparatively early stage in the history of the complicated molar teeth of the 

 Ungulata (especially evident in the Condylarthra) and even of the Proboscidea 

 (Moeritherium). Herein may be recognized a suggestion of parallel lines of 

 evolution. 



3 This conclusion is based on the examination of the teeth of an extinct Primate, 

 viz. Anaptomorphus. Cf. Osborn, 1907, Pig. 38. 



