28 



EVOLUTION OF MAMMALIAN MOLAR TEETH 



FIG. IS. a. Peramus(Sp,lacotherium) minus Owen. Internal view of left mandibular ramus. 

 6. P. (LeptocJadus) dubius Owen. External view of left mandibular ramus. c. P. tenuirostris 

 Owen. Outer face of anterior portion of left ramus. Also, second molar of Amphitherium 

 Prevostii Owen, internal view, and second molar of P. minus, enlarged from fig. 1 a above; 

 internal view, pi-, protoconid ; pa, paraconid ; me, metaconid ; hy, hypoconid ; nig, Meckelian 

 groove. Much enlarged. 



FIG. 19. Enneoilon, Family Diplocynodontidse. Upper Jurassic, America. External view. x-j. 



After Marsh. 



d- 



FIG. 20. Diplocynodon, Family Diplocynodontidse. Upper Jurassic, America. External view. xf. 



After Marsh. 



FIG. 21. Ztocodow, Family Diplocynodontidse. Upper Jurassic, America. Internal view. xf. 



After Marsh. 



Jurassic Pantotheria or Trituberculata. Lower Jaws. Amphitheriidse (Fig. 18) 

 and Diplocynodontidse (Figs. 19-21). For scale see Fig. 4. 



