Abstract: 1600 skulls were observed. The appearance rate of interparietals is 2.94%. All the in- terparietals appear above the superior nuchal line, and 27.6% of them cross over the highest nuchal line. The upper parts of occipital squama of 60 fetal skulls of 7—38 weeks were studied, ossifications were developing around two centers in the form of endomembranous. The author holds that the formation of interparietals resulted from the failure of the transverse occipital fissure to fuse together and the forming of the abnormal ossified center. The author also suggests that the fusion between the superior region and the inferior region of the occipital squama occurs above the superior nuchal line. Both the superior and the highest nuchal line should not be considered as the fusing line o￡ the two regions.

Key words: Interparietal bone； Transverse occipital fissure; Superior nuchal line； Highest nuchal line