In these few lines concerning stereotaxic surgery we wish to emphasize two main points in the methode of stereotaxic localisation which we have described in our Stereotaxic Atlas of the Globus Pallidus: (1) the use of base-lines and (2) the areas of localisation. (1) The base-lines. The method of localisation which we have suggested appears at first sight to be rather complicated. Actually it makes use of two groups of lines: (a) The primary base-lines are intended to provide an easy and precise method for locating in space, not only the corpus striatum but also the thalamus and the hypothalamic region, by reference to a plane passing through the ventricular system. This method therefore produces a consistent localisation and a general method of orientation for the globus pallidus and the adjoining structures. It is, in our opinion, a great advantage of our system (which we first described in 1952) that it employs particular, but separated portions of the ventricular system. (b) The numerous secondary base-lines also have a precise function. The antero-posterior subdivisions allow a proportional localisation in the long axis of the structures and this reduces very greatly the gamut of variations which is inevitable when the localisation is made by reference to a point or to an axis. The horizontal subdivisions are formed by equally spaced lines parallel to the bicommisural base-line. These allow a proportional localisation of the structures in the vertical direction. These various base-lines make it possible to build up definitely localised regions and to show clearly the inter-relationship between the different parts. (2) Areas of localisation. The location of deep cerebral structures has been achieved by different authors, either by giving numbered co-ordinates relating to a selected point, or by defining the smallest area occupied by a structure, by the superimposition of similar sections originating from different anatomical specimens. This usual appearance of structures is valid only for one level of the structure, namely the one traversed by the line of section. The selected position is usually that which is the most favourable in the three planes. This method has the disadvantage that it does not take any account of the changes in shape according to the different levels of the cut. This determines the relationships very poorly, unless one increases the number of planes of section very considerably. Another, much easier method is to “frame” the brain sections in a millimetre scale. The location of structures is then easy. The relation of each structure is shown clearly on each section. In this method, there is no conformity between successive sections, any more than there is between sagittal and coronal sections. Besides, this method of localisation gives a misleading idea of the actual anatomy and its variations. Unless there is a lucky and fortuitous agreement between the living brain and the model, the target theoretically located on the model will not be reached. We have emphasized at some length in our book, the importance of the variations in size and position of the different structures investigated. We have considered it essential to have a more three-dimensional concept of the problem and have interested ourselves in presenting a solid conception of these structures, built up from serial sections in a sagittal and coronal plane. In order to present this solid conception we have chosen areas of localisation conceived in relation to our primary and secondary base-lines. They derive from geometrical figures which are artifical and do not have fixed aspect. It is possible to think of others which might be more complete or more accurate, but which may have impaired the general uniformity of the system of location. The shapes which we have suggested have been chosen so that one may locate with certainty and clarity any structure and its immediate relationships. These areas of location are always placed in the interior of the particular structure, but not always in the same part of that structure. They extend through the whole of the structure and not only along certain selected planes of section. They do not indicate the shape, but give the general location (orientation) of these structures. They seek to display the form of the structure in relation to the two planes commonly used in radiology. The lateral view (vertical to the sagittal plane) enables one to locate a considerable amount of the structure, because the localisation in this plane is greatly facilitated by our system of “base-lines”. In the antero-posterior view (vertical to the coronal plane) the areas are of smaller size, because of the system of localisation which we have been compelled to use (using the mid-line) and the uncorrected significant variations which result from it. The areas of localisation derived from the antero-posterior view can be used through the whole extent of the areas derived from the lateral view. By taking the two together it is possible to imagine quite easily a volume of tissue which is entirely placed inside the structure. This gives quick, accurate and a easy information on the problem. It has been called “the available surgical mass” of a given structure. Although at first sight this method appears complicated it is actually an attempt towards systematisation and therefore towards simplification of the anatomy of the basal ganglia. It has produced a genuine stereotaxic anatomy, which has been developed purely for its use in neurosurgery. Die Verfasser haben in dieser kurzen Übersicht erneut die beiden Hauptpunkte der stereotaktischen Lokalisation behandelt, die sie schon in ihrem Atlas der Stereotaxie der Basalganglien dargestellt haben. Dies sind: 1. Das System der...