we examined the status of the first metacarpal bone whose shape, fetal and post-natal development correspond to those of the thumb proximal phalanx. galen already described this, circa 170 ce. our radiographic data confirm that the pre-axial (radial or anterior) side of the hand matures, later than the post-axial (ulnar or posterior) side, both, pre- and post-natally. a new perspective on thumb primate and human ontogeny is discussed and comparative observations on the evolutionary development (evodevo) of the thumb and the first toe are proposed along with a nomenclature honoring galen's original proposition.
