Delayed carpal ossification in Notophthalmus viridescens Efts: Relation to the progress of mesopodial completion in newt forelimb regenerates.

The persistence of cartilage in the adult newt (Notophthalmus viridescens) forelimb skeletal regenerate has recently been reported by Libbon et al. It is particularly evident in the carpal group, which remains cartilaginous for at least 9 months while all other regrown skeletal parts are either ossified or ossifying. The present investigation was undertaken to determine whether delayed ossification in the adult regenerate recapitulates a pattern evident during the development of the forelimb of the red eft (N. viridenscens' immature terrestrial phase). Right upper limbs of 20 efts were examined at low magnification to establish carpal composition and organization. Among five efts of the smallest size (26.54 plus or minus 2.20 mm snout-to-vent length), and displaying bright orange dorsal skin coloration, all carpal rudiments were cartilaginous. Eleven efts, intermediate in length (33.88 plus or minus 0.81 mm), displaying orange-green coloration, all carpals had ossified. These observations demonstrate that during adult newt forelimb regeneration, the failure of the carpal elements to begin ossification in synchrony with other regrown skeletal parts duplicates a similar schedule of delayed mesopodial ossification which is evident during the development of the red eft's forelimb.