322 The American Naturalist. (April, 
our attention to the skeleton, it is known that almost every 
part of it is the seat of variations of greater or less significance. 
Much importance attaches to the dentition. Many years 
ago, Owen’ called attention to the fact that in the dark races 
the roots of the last superior molar are distinct from each 
other, while in the Indo-Europeans they are known to be more 
or less fused together. These now well-known characteristics 
of human dentition constitute one of the examples of transi- 
tion from a simian to a human type. I have pointed outa 
corresponding modifigation in the structure of the crown of! 
the superior true molars, viz: the transition from a quadri- ~ 
tubercular to a tritubercular structure in passing from the 
lower to the higher races. As this point has some interesting 
implications in the earlier phylogeny of man, and as its value | 
has been disputed, I give it a little attention. | 
The facts of the case are as follows: I have demonstrated’ 
the fact that all forms of dentition exhibited by the Eutherian | 
Mammals have been derived from a primitive tritubereular : 
type. Professor Osborn says that he expects to be able to do 
the same for the Multituberculate (? Prototherian) dentition. | 
I have also shown that man exhibits a tendency to revert 
from his primitive quadritubercular molar to this tritubercular 3 
type.’ These facts are now common knowledge among paleon- 
| 
tologists, although Dr. Brinton states in one of his late works 
that the latter proposition has been “refuted ” by Dr. Harrison 
Allen and Professor Virchow. As to the significance of these 
facts, I have expressed the view that this acquisition of a tri- 
tubercular molar is a reversion to the lemurine type. This 
conclusion is necessary because the lemurs are the last of 
the families in the line of the ancestry of man which pre- 
sent this dentition. The monkeys and anthropoid apes are all 
quadritubercular, except a few limited collateral branches of 
the former, which still retain the lemurine type. There are i 
also a few collateral types of lemurs which have acquired one 
* Odontography, 1840-5, p. 454. 
Amer. Philosoph. Soc., Dec, 1883; Origin of the Fittest, 1887, PP- 
2 Proceeds. 
245, 347, 359. 
3 Amer, Journal of Morphology, II, 1888, p: 7. 
