1879.] NATURAL SCIENCES OP PHILADELPHIA. 193 



General Observations. 



In both Canidse and Felidse 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 

 Canidse, while Smilodon and Lynx exhibit the anterior reduction 

 in Felidse. 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 Canidse. 



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. 1 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 twent} f -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 Hominidse 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. 



