THE ONE BIG DIGIT OF THE HORSE 251 



arrangement and number, what shall we say of the liability to varia- 

 tion in individuals and races, separated from each other perhaps by 

 millions of generations, and subjected to different nervous influ- 

 ences, and to the action of different surroundings ? 



It is evident to me that in many instances homologies are rather 

 assumed than proved ; and it will be seen how difficult it may be 

 to determine in all cases what particular bone in the hand or foot 

 of one animal is homologous with another bone in the hand and 

 foot of another animal. 



Therefore we cannot always be ' cocksure ' that in these cases 

 our inferences are beyond question. 



Professor Huxley says, ' In matters of the intellect do not 

 pretend that conclusions are certain which are not demonstrated or 

 demonstrable.' 



We have now to face four cases of abnormalities, which may 

 interfere with the notion that there is, as Chauveau and others 

 think, such a thing as an archetypal hand or foot with jive digits. 

 These are as follows : 



A. In Chauveau's work 1 are given two instances of abnormal 

 hands in Horses, a sketch of which is shown in Fig. 90. There can 

 hardly be much doubt that these so-called monstrosities are only 

 reversions (at least they might be so interpreted) to some very 

 remote type from which the Horse descended, the Ox and its 

 congeners having continued that remote line of type up to the 

 present day. 



We might suppose that while the hand and foot of the Horse 

 have become consolidated throughout into one digit, those of the Ox 

 have become consolidated only as far as the metacarpal and meta- 

 tarsal bones, leaving the phalangeal portions of the two digits free. 



I do not see how we can escape from some such conclusion as 



1 Anatom. Compar, des animaux domesliques, p. 130. 



