Figure 7: A diagrammatic representation of different types of skeletal integration observed during salamander limb regeneration.

(A) The original limb was amputated mid-stylopod, through the radius and ulna, and allowed to regenerate under various experiential conditions, resulting in different types of skeletal integration. (B) Under normal circumstances the regenerating axolotl limb will connect seamlessly with the existing stump tissue resulting in an overall structure that matches the original precisely. Specific surgical manipulations can, however, result in failed integration between the stump and the regenerate. (C) As seen with the accessory limb model, there is a disconnection between the stump and regenerated bone tissue (Endo et al. 2004). Exogenous RA treatment of blastema tissue frequently results in (D) the formation of an ectopic skeletal element between the stump and regenerate or (E) a fused connection that gives rise to a novel structure relative to the original pattern (Maden 1996). (F) In the current study, exogenous vitamin D treatment induced an abnormal fusion between the stump and regenerated skeletal element, resulting in a “seamed” (visible point of) integration. Red arrowheads represent the plane of amputation.