Frankfort horizontal plane
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1. a line approximating the base of the cranium, passing from the infraorbital ridge to the midline of the occiput, intersecting the superior margin of the external auditory meatus; the cranium is in the anatomic position when the base line lies in the horizontal plane and right and left sides are level.
2. a standard craniometric reference plane passing through the right and left porion and the left orbitale; drawn on the profile radiograph or photograph from the superior margin of the acoustic meatus to the orbitale.
Frankfort horizontal plane(frănk′fort)
A cephalometric plane joining the anthropometric landmarks of porion and orbitale; the reproducible position of the head when the upper margin of the ear openings and lower margin of the orbit of the eye are horizontal.