1004 The American Naturadist. [December, 
a primitive character, Again, it is found throughout all the 
Primates, and although seldom availed of, this cusp constitutes 
an important and distinctive character as between the differ- 
ent races of man. Its extreme antiquity is appreciated by few 
anthropologists, and at the present time it is degenerating. 
(See Figure 8). 
__-protoconid \ _ Protoconid 
Fig. 8.—EPITOME OF THE EVOLUTION OF THE HUMAN MOLAR TEETH. 
1. Reptile. 2. Dromatherium. 3. Microconodon. 4. Spalacotherium. 5. 
Amphitherium. 6. Miacis. 7-8. Anaptomorphus. 9-12. Various Primates 
11-12. Homo. A succession of molar types, not of ancestral types. 
While these changes were taking place, the upper molars 
remained comparatively stationary in the persistence of the 
simple trigon, up to the close of the Cretaceous period, the 
main change being a depression of the level of the trigon. All 
three cusps in some groups were depressed from the high 
secodont to the low bunodont level. In the majority of the 
carnivorous types we find that only the protocone was de- 
