The term interaural line refers to a basic stereotaxic landmark for brain surgery in the days before noninvasive methods made possible the visualization of internal features of the living brain. The zero point of the stereotaxic space was that where the interaural line (the straight line between the points of earbars in the external auditory meatus of each ear) intersected the midsagittal plane (the vertical plane between the two hemispheres) and the orbitomeatal plane (the horizontal plane defined by the interaural line and the inferior surfaces of eyebars at their points of contact with the inferior margins of the orbits.
The zero plane of the Horsley-Clark stereotaxic apparatus, on which the brain atlases of most nonhuman primates was based, was by convention parallel to and 10mm above the horizontal plane of the interaural line ( Clarke-1920 ). Since the advent of ventriculography and magnetic resonance imaging the basic stereotaxic landmark is the bicommissural line ( Martin-2000 ).
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