158 



EVOLUTION OF MAMMALIAN MOLAR TEETH 



condition, stages which have already been treated in the evolution of 

 the human molar teeth (pp. 50, 55). 



The special characters of this evolution were brought out in the 

 same paper. An interesting feature of some of these American 

 Eocene monkeys 'is that some of them pass from a tritubercular into 

 a quatlri- and finally into a sexitubercular condition, with a prominent 



ml:- 



ml:- 



Vic,. 128. Superior molars of (A) Adapis maynus, a lemuroid from the Eocene of France; 

 (B) Hi/opsodus uintrnsis, an Insectivore (?) from the Eocene of North America ; and (C) Notharctvs 

 sp., a Primate, from the Eocene of North America ; all three apparently derived from the same 

 tritubercular ground plan, by the upgrowth of the hypocone. A and B, x^. 



hypocone and large intermediate tubercles, closely homoplastic with 

 the grinding teeth of primitive Ungulates (Figs. 132, 149). Similarly 

 the premolars progress by the addition of internal cusps. 



The normal dentition of man is beautifully illustrated in Figs. 1 and 

 134, p. 161, taken from Selenka's admirable monograph. 1 In modifying 

 his figure (Fig. 1) we have expressed the tritubercular homologies on 

 one side of the jaw and the embryonic order of evolution of the cusps 

 in numerals on the opposite side. In this connection reference may be 



FIG. 129. Skull and dentition of a Lower Eocene (Wasatch) Primate Anaptomorphv* 

 homunculus, with tritubercular upper molars. Partially reconstructed. The premaxillary portion 

 of the skull is wanting, x^-. 



made to the discussions of the relative value of embryological and 

 palaeontological evidence on pp. 49, 214. 



Certain peculiar variations of the human molar teeth may be referred 

 to here which are often described by anthropologists as anomalies, but 

 which really are either homogenetic or homoplastic with cusps well 

 known in the lower mammalia. 



Protostylc or tdbercvlus anomalus. On the anterior side of the 

 protocone in the upper molars we have observed in many of the lower 

 mammals, especially in the Periptychidse (Periptychus, Ectoconus, 



Menschenaffen, Wiesbaden, I'.Mio. 



