36 MICROSCOPIC ANATOMY OF THE TEETH 



level of the posterior portion (talonid) while retaining all 

 of its (three) cusps '. Fig. C 2 shows the arrangement of 

 the cusps in Anaptomorphus , the oldest lemur known, the 

 cusps coloured red representing the fully developed trigonid 

 in the first and second molars, but in the third molar the 

 paraconid has disappeared. In this animal we have a six- 

 cusped tooth representing, in the first and second molars, 

 the three cusps of the trigonid and the three of the talonid. 

 In the third molar the six cusps are -made up of two of the 

 trigonid and four of the talonid. 



Trigonid In man the trigonid is represented by the protoconid and 

 an ' metaconid only, the paraconid being suppressed, and the 

 five cusps are made up of these and three cusps of the 

 talonid the hypoconid, entoconid, and hypoconulid (fig. C 3 ). 



Lower Molars. 



Anterior buccal Protoconid ~\ Primitive triangle or 

 Anterior lingual Metaconid / Trigonid. 

 Posterior buccal Hypoconid ^ 



Posterior lingual Entoconid > Primitive heel or Talonid. 

 Posterior mesial Hypoconulid J 



Origin of Scott (22) claims that the premolars have arisen by a 



premolars. (jjg eren ^ p roce ss from the molars, and considers that the 



internal cusps of these have arisen from the cingulum. 



Cope considers that this may show ' the origin of two 



identical structures by different evolutionary routes '. 



Among the many critics of the tritubercular theory, 

 Forsyth Major (15) considers that the advocates of tri- 

 tuberculism have failed to show that the mammalian molar 

 can be traced back to a more and more simple form, and is 

 Polybuny. of opinion that it can be traced to a polybunous or multi- 

 tuberculate form, and that the real tritubercular pattern is 

 a more specialized secondary stage. He states that in the 

 lower Eocene strata, multitubercular teeth are found side by 

 side with the simpler forms. He would, therefore, consider 

 that the tritubercular teeth are reduced and modified forms 

 of earlier multitubercular molars. 



Ameghino considers the tritubercular form to be ' the 

 result of the simplification of molars which were formerly 

 more complicated '. 



