A stereotaxic map of the bony tentorium of the cat.

THE bony tentorium cerebelli of the cat lies between the cerebellum and the cerebral hemispheres. Since its exact location and size are not indicated in the major atlases [ 1, 2, 3, 4, 5], its discovery often comes as an unpleasant surprise to investigators attempting to explore brain stem or cerebellar areas with depth electrodes or cannulae. A direct hit may destroy both the electrode being positioned and the surrounding brain tissue. Contact with the edge of the tentorium can produce an electrode deflection that goes unnoticed until the brain is subjected to histological analysis. Therefore, as part of a larger program of brain stem exploration in our laboratory, it became desirable to map the exact location of the bony tentorium. This map allows us to determine when orthogonal coordinates can be used for brain stem exploration and what the optimal angles of approach are when non-orthogonal coordinates must be used.