54 



VARIATION 



has the usual number of digits, but the thumb has three instead 

 of two phalanges, though its general shape is normal. In the 

 left hand there is much confusion in the region of the thumb. 

 There is an extra digit, but its true character is not so evident. 

 It is sharp, like a finger, but functions as a thumb. Internal to 

 this is a thumblike supernumerary with a true nail, but from 

 its position it is functionless (see Fig. 9). 



FIG. 9. Meristic variation in the hand : right and left hands of the same indi- 

 vidual, showing on the left hand a duplication of the forefinger at the 

 expense of the thumb, and on the right hand an extra joint in the thumb. 

 After Bateson 



A fifth real finger, making six digits in all, is not uncom- 

 mon. Its true position, however, is by no means always easy 

 to determine. 



Speaking generally, extra digits may arise in three ways, 

 either by addition to the series of an outside member next the 

 thumb or the little finger, by the insertion of a member at some 

 point within the series, or by the doubling of a member. Just 

 which has taken place in any given case is not always easy to 

 determine. 



Reduction in the number of digits is common and takes place 

 in three ways, by the loss of an outside member (generally 



