THE TEETH OF VERTEBRATES 



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Fig. 17. — Phyletic History of the Molar Cusps. (After Osborn.) 



a, The Reptilian stage. (Haplodont.) 



b, Early Mammalian stage. (Triconodont. ) 



c, Triangular stage. (Tritubercular molar.) 



d, Quadritubercular molar. 



