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A point on the sagittal suture of the skull in line with the parietal foramina.
Late 19th century. From French obélion from Hellenistic Greek ὀβελιαῖος (given in Broca's paper as ὀβελαῖος) sagittal (from ancient Greek ὀβελός + -ιαῖος, suffix forming adjectives) + French -ion.