158 PRIMARY FACTORS OF ORGANIC EVOLUTION. 



hallux opposable, while 

 in the Hominidae the 

 hallux is not opposable. 

 This is not a strong 

 character, since it de- 

 pends on a slight differ- 

 ence in the form of the 

 entocuneiform bone. In 

 some vertebrates, as the 

 tree-frogs, the same and 

 similar characters (ge- 

 nus Phyllomedusa) are 

 not regarded as of fam- 

 ily value. It is then 

 highly probable that 

 Homo is descended 

 from some form of the 

 Anthropomorpha now 

 extinct, and probably 

 unknown at present, al- 

 though we do not yet 

 know all the charac- 

 ters of some extinct 

 supposed Simiidae, of 

 which fragments only 

 remain to us. It cannot 

 now be determined 

 whether man and the 

 Simiidae were both de- 

 scended from a genus 

 with opposable hallux, 

 or without opposable 

 hallux, or whether from 

 a genus presenting an 



Fig. ^i.— Tomitherium rostratum Cope, 

 five-sixths natural size ; a, ilium ; h, femur. 

 Original. 



