Morphogenesis of the carpal elements in the regenerating forelimb of adult Notophthalmus viridescens viridescens.

This study is concerned with the morphogenesis of the carpal elements in the regenerating forelimb of the adult newt. Blastema cells surrounding the remnant bony stumps begin to differentiate into cartilage on the twentieth post-amputation day. Subsequently, masses of carilage build up from the radial and ulnar stumps. The radial mass is larger and differentiates more rapidly than the ulnar mass. By the fifty-fifth post-amputation day, the eight basic carpal elements are formed, with fusion of two of the units, intermedium with ulmare, occurring by the seventieth day. The completed regenerate possesses the seven carpal elements characteristic of the normal adult limb. The present results show that during limb regeneration in the adult newt the carpal elements are restored to their original number and position and that the pattern of such carpal differentiation proceeds in a proximodistal direction influenced by the stump remnants of the radius and ulna.