By means of histomorphometric analysis of temporo-spatial changes of the thickness of oral maxillary epithelium in day 11 and 12 ICR, Swiss, and DBA/2 x B6 mouse embryos, the transitory existence of two potential tooth anlagen was documented. The mesial primordium appeared slightly later and disappeared earlier than the distal one. Their development culminated at dental lamina and bud stage, respectively. These potential vestigial tooth anlagen might correspond to the third and fourth upper premolars present in some recent rodent families and in Paramyidae, the supposed ancestors of actual rodents.