Axial characteristics of nerve induced supernumerary limbs in the axolotl.

Supernumerary limbs were produced by deviating the sciatic nerve to the surface of the axolotl hindlimb either alone or in combination with small skin grafts from specific limb positions. With no skin grafts a very low frequency of good supernumeraries were produced. However, when associated with skin grafts, this frequency was significantly increased. The pattern of skeletal elements and muscles were analysed in the supernumeraries which formed at each location. In both the anterior-posterior and dorsal-ventral axes specific anatomical features were found which correlated with their position of origin on the host limb. Characteristic features were also observed with respect to the proximal-distal axis of the outgrowths. These phenomena are discussed in relation to our current understanding of the rules of pattern regulation in the regenerating limb.