The central point on the upper margin of the external auditory meatus; as a cephalometric landmark, it is located in the middle of the metal rods of the cephalometer. [G. poros, a passage]
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po·ri·on 'pōr-ē-.än n, pl po·ria -ē-ə or porions the midpoint on the upper margin of the external auditory canal
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po·ri·on (porґe-on) [por-1 + -on neuter ending] a craniometric landmark, being the most lateral point on the roof of the bony external acoustic meatus, vertically over the middle of the meatus. Called also point Po.Medical dictionary. 2011.