Digit identity frameshift hypothesis ($C_{\mathrm{II}},C_{\mathrm{III}},C_{\mathrm{IV}}\mapsto D_{\mathrm{I}},D_{\mathrm{II}},D_{\mathrm{III}}$)

The classical avian hypothesis that anatomical digit identities I, II and III are expressed at positional condensations II, III and IV. It distinguishes position from developmental identity; evidence for a limited anterior shift does not require invariant identities for every posterior anatomical digit.^[ref]