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THE PHYSIOLOGY OF TWINNING 



5. A case of complete double hand with perfect 

 mirror-image S3anmetry is described by J. J. Murray. 

 This hand, shown in Figure 71, appears to have been 

 completely bilaterally S3mimetrical and without thumbs, 



Figs. 68-71. — Various degrees of duplicity (twinning) of the human 

 hand. Fig. 68, a hand with a thumb like a little finger. Fig. 69, a hand 

 with thumb represented by two fingers. Fig. 70, a hand with thumb 

 represented by three fingers. Fig. 71, hand completely twinned with 

 the thumb represented by four fingers which are mirror images of the 

 fingers in the radial component. (After Bateson.) 



a whole set of four fingers having arisen in the place 

 of a thumb. The two sets of four were physiologically 

 equivalent in use and value. I look upon this case as 

 the logical culmination of the series. If our theory is 

 correct, that the plane of symmetry in the vertebrate 



