Polydactyly, Related Defects and Axial Shifts-A Critique

Data are presented which show that the hind limbs of diplopod chick embryos (a polydactylous mutation) are one vertebra further anterior than normal. No displacement of the hind limb was encountered in a polydactylous pigeon mutation or in the duplicate mutation of chickens. Carter's hypothesis for the development of the luxate syndrome of mice is discussed and criticized. It is shown to be incompatible with known facts about limb development; and an alternate hypothesis is advanced, which postulates that polydactyly and related defects result from relatively late deviations in the distribution of an hypothetical ectodermal ridge maintenance factor believed to be present in limb bud mesoderm.