Human brains present a clear asymmetry of the postero-lateral cortical area, so called "planum temporale" (Geschwind and Levitsky). This asymmetry is on favour of the left brain. A similar asymmetry is observed on the parietal operculum. MRI studies of 37 healthy volunteers have shown a clear difference between individuals. Mixing the index of temporal and parietal asymmetry, the authors consider four types: the most frequent pattern concerns 90% of right handed. For the others, 10% there are left handed as right handed. On conclusion, planum as many asymmetry and opercular asymmetry can be divergent, and both canan to determines handedness.