944 On Lemurine Reversion in Human Dentition. (November, 
building up, or addition of the posterior internal cusp. Some 
justification for a light estimate of its value may be found in the 
following tables. But it must be remembered that it is not always 
possible to determine exactly the race of the person represented 
by a skull even when care in its identification has been exercised. 
Emigration and war have constantly rendered races impure, and 
transplantation on a large scale has in some parts of the earth 
produced hybrid races. The results of a study of human crania 
. are sure to be more or less vitiated by these circumstances. We 
obtain averages rather than exact definitions. Nevertheless the 
extremes of the series of variations are likely to be found to be 
characteristic of established forms of man, and will thus justify 
my belief in the value of the characters presented. To ascertain 
the relation of these variations to the races is the object of the 
present enquiry. 
The cause of the tritubercular reversion belongs to the class of 
agencies active in evolution of organic types of whose real nature 
we know little. It can not be said to be due to a contraction of 
the maxillary arcade, for the Esquimaux and some other peoples 
which display the tritubercular dentition are not deficient in this 
respect. Tritubercular molars do not require less length than the 
quadritubercular, for the external width of the crown is the same 
in both cases. They require less material, however, than a 
quadritubercular crown, since a triangle is smaller than a square 
drawn on the same base line ; however in some men of the lower 
races who present the tritubercular molars, their outline is nearly 
square. The hypothesis advanced! to account for the reduction 
of the number and quality of human teeth observed in the higher 
races, as well as for the replacement of the prognathous Jaw by 
the orthognathous, is that such changes are due toʻa trans erence 
of material and of growth-energy from these parts to the superior 
part of the skull and its contents. The relative superiority of the 
dimensions of these latter parts in the higher races is supposed af 
account for the reduction of size of the jaws. 
Mas | 1 f, $ Į sented by 
In the followin be formu 
numbers. Only the last three, or the true molars, in each jaw pei 
sidered. Tubercles of reduced size are represented by fractio 
it? al 
7 Thus DEN indicates that each superior molar is quadrituberculat, 
_ and each inferior molar quinquetubercular. This represents Ne 
_ extreme of the series represented by the lowest races- 
roceeds. Amer. Philos. Soc., 1871, p. 252. 
