free ends 16 free ends 16 of legs 14 define a triangle lying within a defined plane drill guide 10 further includes guide means for guiding the drill in a direction perpendicular to the plane defined by the triangle formed by legs 14 and through the geometric center thereof the guide means comprises a tubular member 18 extending through platform 12 in a direction perpendicular to the triangular plane described above tubular member 18 is hollow defining a central lumen to permit the passage therethrough of a drilling device described in the u s pat no 4 931 056 the diameter of this lumen is not critical but it must at a minimum be sufficient to permit the passage of the drill in accordance with the invention tubular member 18 is further provided with a drill guide slot or opening 20 the drill guide slot or opening 20 allows the neurosurgeon to have direct visual access to the drilling point this visual access allows the neurosurgeon to more accurately place the drill and also to maintain the drill guide 10 in an accurate position relative to the hole in the cranium for catheter placement when drill guide 10 is placed on the patient 39 s cranium with the free ends 16 of legs 14 resting thereupon the plane of the triangle defined by free ends 16 coincides with or is parallel to a plane tangent to the cranial surface directly below tubular member 18 accordingly drill guide 10 directs the drilling device perpendicular to this tangential plane ensuring the production of a burr hole through the cranial bone at an angle of 90 degrees to the surface of a plane tangent to the cranium this alignment assures that a ventricular catheter inserted into the brain in.