26 
General Observations. 
In both Canidx and Felidx the reduction of the dental series 
is connected with a contraction of the facial part of the skull, 
either posteriorly or anteriorly. Enhydrocyon is an example of 
anterior abbreviation, and Icticyon of posterior contraction among 
Canidex, while Smilodon and Lyn« exhibit the anterior reduction 
in Felide, I have already pointed out that this reduction is ac- 
companied by a corresponding increase in the size of the sectorial * 
teeth. But the reduction in the number of teeth,in geologic time 
has not been confined to the Carnivora, but belongs to the Ungu- 
lates and Primates as well. The small number of teeth is gene- 
rally associated with high specialization among Mammalia gene- 
rally. The genera Synagodus and Dysodus are the most special- 
ized of the Canide. 
I may here refer to the frequently observed reduced dentition 
of man. Darwin first pointed out the significance of the absence 
of the third molars from the standpoint of evolution, citing Ame- 
rican cases; and I have observed the similar bearing of the ab- 
sence of the external superior incisors.'. These reductions are 
very frequent in the United States, and probably elsewhere among 
civilized nations, but statistics on this point are yet wanting. My 
friend Dr. C. N. Pierce, an experienced and scientific dentist of 
this city, informs me that he knows of twenty-eight families in 
which the external superior incisors are absent; to these, four 
families may be added, which have fallen under my own observa- 
tion: that the absence of one or both pairs of the third molars 
is still more common, is confirmed by Dr. Pierce’s experience. 
It is evident that we have characters which, if stable, would 
indicate two or three genera of Hominide additional to Homo. 
They are unstable at present; that is, they are not yet invariably 
found in any race or species of man, or, in other words, are not so 
associated with other physical characters as to form a correlated 
index of them. But experience in paleontology and zoology renders 
it almost certain that these dental characters will at some future 
time assume this degree of importance by becoming stable. This 
is already indicated by the fact of their being constant in families 
at the present time. As to what races will be thus distinguished 
1 Proceedings American Philosophical Society, 1871, p. 234. 
