(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. SYN: auriculoinfraorbital plane, eye-ear plane, Frankfort horizontal plane, Frankfort plane, infraorbitomeatal plane.