ATAVISM. 161 



otomized unequally, and is thus more likely to^be 

 erroneously interpreted from a superficial examination. 



Bardeleben has recently attempted most strenuously 

 to prove that the ancestors of modern mammals were 

 heptadactyle rather than pentadactyle, and he bases this 

 opinion on a supposed discovery in the human embryo 

 of some remnants of the missing digits, on the pre- and 

 post-axial side of the foot respectively. In addition he 

 draws attention to the existence in some mammals, 

 chiefly rodents, of an ossicle in the foot, usually regarded 

 as a sesamoid. This Bardeleben regards as 

 vestiges of the missing digits on the inner 

 side of the manus and pes, and terms 

 prepollex and prehallux respectively. On 

 these grounds he would urge that super- 

 numerary big-toes and thumbs are ata- 

 vistic. 



Even supposing the vestiges of such 

 digits to exist as Bardeleben believes, it in the manus 

 would influence but little the views now 



held regarding the nature of bifid thumbs (Modiaedfrom 

 and big toes, for by an overwhelming amount 

 of evidence it can be shown that in man they arise by 

 dichotomy of the digits. 



A full study of the question of supernumerary digits 

 in all its bearings, and the examination of a very large 

 number of specimens convinces me that an excess in 

 the number of digits, in pentadactyle mammals, is due to 

 dichotomy, and can in no sense be regarded as reversion. 

 Supernumerary digits in animals with fewer digits than 

 five are, in some few cases, due to atavism, but in many 



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