MOLAR TEETH OF THE MAMMALIA EDUCABILIA. 251 



inferior series unite, in order to produce the result ; in diyision 

 y the tubercles of both jaws unite entirely across the crown, with- 

 out any distinction between those of the outer and inner sides. 

 Thus the molar type of dentition of the Proboscidians is the most 

 generalized among the Lophodonts, resembling in this respect the 

 type of construction of the feet. 



lY. THE ORIGIK OF THE MODER]S" TYPES OF BUKODOKT AKD 



L0PH0D02iT DENTITIOi^. 



The four types of molar dentition, the Haplodont, Ptycho- 

 dont, Bunodont, and Lophodont, are by no means sharply de- 

 fined, but pass into each other by insensible gradations at many 

 points. The addition of cusps to the simple cone has been 

 accomplished by the appearance of folds at the base of the 

 crown, which have increased in size so as to resemble the primi- 

 tive cusp to which they are attached. As already pointed out, 

 the first additional cusp in the transverse direction appears on the 

 inner side of the first, or anterior cusp. The last one was ap- 

 parently the inner posterior. I first consider the carnassial mo- 

 lars. 



1. Tlie Carnassial Bunodo7its. 



In tracing the appearance of the different types of superior 

 sectorial in time, the following facts are patent : In the Eo- 

 cene genera Mesonyx, AmUyctonus, Oxymna, Stypolophus,* etc., 

 the inner tubercle is much more largely developed than in any ex- 

 isting Carnivora, with the exception of some of the Viverridce. In 

 all, the sectorial crowns are less efficient as shear-like cutters than 

 in Canidce, Mustelidce, Hycenidm, and Felidce, on account of the 

 shortness of the posterior blade and the slight compression of the 

 anterior cone. On the other hand, in all of them the number of 

 teeth presenting the carnassial or three-tubercled type is greater 

 than in existing genera, the posterior upper molars in the latter 

 being either narrowly tubercular or wanting. The genus Hyceno- 

 don, while agreeing with the others in this respect, differs from 

 them in the great reduction of the inner cusp, which is obsolete 

 even in the representative of the true carnassial tooth, although 

 the inner root remains in all. Hence this type of dentition might 

 be regarded as the most specialized of those of the Carnivora, 



* In the original, the synonym Prototomus is used here. 



