48 PROBLEMS OF GENETICS 



to divide, the normal separation of the median digits of the foot 

 being suppressed. 



Webbing between the digits, in at least some of its mani- 

 festations, is a variation of similar nature. The family recorded 

 by Newsholme 12 very clearly shows the dominance of this con- 

 dition. The case is morphologically of great interest and must 

 undoubtedly have a bearing on the problems of the mechanics 

 of Division. In discussing the phenomena of syndactylism 

 I pointed out some years ago that the digits most frequently 

 united in the human hand are III and IV, while in the foot, 



a 



_ m+in 



'v 



FIG. 4. Case of complete syndactyly in the foot. 77 and 777, digit apparently 

 representing the index and medius. c 2 + c s , bone apparently representing the 

 middle and external cuneiform; cb, cuboid; c l , internal cuneiform. (After Gruber.) 



union most frequently takes place between II and III. 13 In 

 Newsholme's family the union was always between II and III 

 of the foot, except in the case of one male who had the digits 

 III and IV of the right hand alone webbed together. There 

 can be little doubt that the geometrical system on which the 

 foot is planned has an axis of symmetry passing between the 

 digits II and III, while the corresponding axis in the hand passes 

 between III and IV. Union between such digits may therefore 

 be regarded as comparable with any non-division or " coalescence " 

 of lateral structures in a middle line, and when as in these ex- 



12 Newsholme, Lancet, December 10, 1910, p. 1690. 

 18 Materials for the Study of Variation, 1894, p. 358. 



