358 MERISTIC VARIATION. [part i. 



the fact that the division of digits in the lowest forms of polydactylism 

 appears also first in the peripheral phalanges. These phenomena appear 

 to be in contradiction to each other, and I am not aware that the fact 

 of the appearance of the digits early in the development of the limb 

 throws any light on the difficulty. 



The number of digits which may be thus united is not limited to 

 two, and examples of intimate union between three and even four digits 

 are common. 



The position of union. 



*527. Those who have treated of this subject do not, so far as I am aware, 

 notice the fact that the phenomenon of Syndactylism most frequently 

 affects particular digits. From an examination of the recorded cases 

 it appears that in the hand there is a considerable preponderance of 

 cases of union between the digits III and IV. I regret that I have 

 not material for a good analysis of the evidence on this point, but I 

 may mention meanwhile that in a collection taken at random of some 

 thirty-five cases of hands having only two digits united (chiefly those 

 given by Fort and Axsaxdale) over 25 are cases of union of the digits 

 III and IV ' • in only one were the digits I and II united ; the digits 

 II and III in 1 4 cases ; the digits IV and V in 1 3 cases. 

 *528. On the other hand if two digits in the foot are united they are 

 nearly always II and III. 



If in the hand three digits are joined they may be either III, IV 

 and V, or (perhaps less commonly) II, III and IV. In cases of union 

 of all the digits II to V, the digits III and IV are often much more 

 intimately united than the others, and are often recorded as having a 

 common nail, while II and V have separate nails. 



This question of the comparative frequency of the different forms of 

 syndactylism would probably repay full investigation, and to the study 

 of the mechanics of Division it would clearly be important. In the 

 meantime may be noted the fact that the evidence suggests the possi- 

 bility that we have here to do with a case of union of parts which are 

 related to each other as optical images, and that the digits II to V of 

 the hand constitute an imperfect Minor Symmetry within themselves. 

 The fact that the subjects of most frequent union in the foot ai'e the 

 digits II and III, not the digits III and IV as in the hand, may be 

 connected with the fact that the hallux stands to the foot in a different 

 geometrical relation from that which the pollex bears to the hand and 

 that consequently the axes of Symmetry are different in it. 



(3) Absence of digits (Ectrodactylism). 



In the conditions already described though the digits are not all 

 clearly divided from each other yet no one whole digit can be supposed 

 to be absent. Even in the specimen shewn in Fig. 104, II, from the 

 presence of separate metacarpals III and IV the identity of the several 

 digits is still easily recognized. These simplest cases however by no 

 means exhibit all the phenomena. From a large group of cases the 

 three following are chosen as each illustrating a distinct possibility. 



1 Owing to the ambiguity of some records as to the similarity of the condition 

 in the right and left hands I cannot give exact numbers. 



