Homologous (Resonance-like) Function in Supernumerary Fingers in a Human Case

Abstract

In amphibia, a supernumerary muscle during spontaneous and reflex activity contracts simultaneously with the homologous normal muscle of the same name. 1 Since this is true for each individual muscle, a supernumerary limb (or limb fragment) always exhibits the same movements as the nearby normal limb (or corresponding limb fragment) of the same side. 2 From this phenomenon has been derived the concept of a “resonance-like” principle of communication in the nervous system. 3 The experimental evidence has been confined, thus far, to the amphibia, where supernumerary limbs can be produced at will. In order to test the validity of the principle of homologous (“resonance-like”) response in higher vertebrates and man, where the transplantation of supernumerary limbs has not yet been possible, we must avail ourselves of those cases in which congenital duplications of limbs or of some of their parts present us with a comparable situation. A human case favorable to such study has recently been described by Halverson and Amatruda, 4 and was re-examined by the author as to its bearing on the problem of homologous function.

The case concerns a girl, L. S., 14 years of age, with congenital duplication of the left forearm and hand. While the radial part of the hand, including the thumb, is absent, its place is taken by a mirror image of the normal ulnar part. The resulting double formation is a symmetrical hand with what appears to be the original index as axis of symmetry and 2 groups of 3 fingers each to either side of this index. The order of the supernumerary fingers being reversed, the 7 fingers of the hand can be identified, beginning with the most lateral one, as (n stands for normal, e for extra fingers) : n5, n4, n3, n2, e3, e4, e5.