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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.
An imaginary cephalometric line from the infraorbital ridge through the middle of the external auditory meatus to midline of occiput.
See also: line