Hensen's node, but not other biological signallers, can induce supernumerary digits in the developing chick limb bud.

The purpose of this study was to determine whether the organizer regions of early avian and amphibian embryos could induce supernumerary (SN) wing structures to develop when they were grafted to a slit in the anterior side of stage 19-23 chick wing buds. Supernumerary digits developed in 43% of the wings that received anterior grafts of Hensen's node from stage 4-6 quail or chick embryos; in addition, 16% of the wings had rods of SN cartilage, but not recognizable SN digits. The grafted quail tissue did not contribute to the SN structures.