THE SIGNIFICANCE IN HUMAN STEREOTACTIC BRAIN SURGERY OF INDIVIDUAL VARIATION IN THE DIENCEPHALON AND GLOBUS PALLIDUS*

Access to deeply seated parts of the brain with minimal damage to structures other than the target itself was achieved in the experimental animal by Horsley and Clarke (1908). A coordinate system was employed based upon three fundamental planes, the mid-sagittal plane, a horizontal plane passing through the external auditory meati and the inferior margins of the orbits (the Frankfurt plane), and a coronal plane through the auditory meati at right angles to the latter. Thus the position of any point in the brain could be defined by three coordinates related to these three planes.