THE TEETH 457 



blade being formed, not by the paraconid and protoconid, but by the 

 paraconid and metaconid. To this view, however, the palreontological 

 evidence is clearly opposed. It might be argued that this cusp repre- 

 sents the beginning of a new external cusp arising from the irritation 

 produced on the outer surface by the small upper tubercular molar, 

 and, further, that the tritubercular type of molar was in this way de- 

 veloped from the simple haplodont type, by the addition to a primitive 

 single cusp in the position of the paraconid or metaconid of an ex- 

 ternal cusp in the position of the protoconid. There is no evidence 

 to support this theory, and it cannot be supposed that the upper molar 

 now so greatly reduced in size could produce so marked an effect upon 

 the lower molar. 



