148 



EVOLUTION OF MAMMALIAN MOLAR TEETH 



Fin. 111. Side view of the skull and jaws of Eutypomys thomsoni (cf. Fig. 110) showing sub- 



hypsodont cheek teeth. 



FIG. 112. Skull of the Rat (Mus rattux), illustrating the type of dentition characteristic of the 

 Myomorph Rodents. The motion of the jaw is proa], i.e. from in front upward and backward, x j-. 

 After Matthew. 



DUPLICIDENTATA. 



In the Duplicidentate Koclents (or Eabbits, Hares, and Pikas), 

 otherwise known as Lagomorpha, the crown has undergone a complete 



p. 2 3 4 m'.l 2 3 



FIG. 113. Skull of Palaolagus intermedius, an ancestral Hare from the Oligocene of Colorado, 

 illustrating the upper dentition of the Duplicidentate Rodents, x y. After Matthew. 



metamorphosis into hypselodoiit, columnar and rectangular form. These 

 specialized adult crowns show no trace of separate tubercules or of 

 anything but a strictly transverse pattern, yet where the permanent 

 teeth are unworn, especially among certain fossil species, we find 



