Skull asymmetry and handedness in adults: a possibility of their association with lateral head turning in infancy.

During the first two to three months after delivery infants when placed in the supine position commonly turn their heads laterally. This posture has been linked to the intrauterine orientation of the fetus. Skulls of adults were expected to bear a mark of this predominant head position in the form of occipital flattening. A blind examination of computerized axial tomography (CT) scans of 35 normal subjects assessed for handedness (20 right- and 15 mixed-handers) confirmed this prediction for the latter group only. Mixed-handers showed a slight, but reliable flattening of the right occiput. Also, there was a small but significant inverse association between the size of the petrous ridge and handedness. Examining subtle variations in skull shape of adults may provide a glimpse into some aspects of pre- and early postnatal development.