The falx and tentorium constitute an important protection against any sudden impacts of pressure by keeping apart heavy portions of the brain, but they also provide an opportunity for trouble in case of swelling or need of displacement.
From the material that has gone through the Neurological Laboratory of the Henry Phipps Psychiatric Clinic, I have selected some cases illustrating various types of herniation under the falx and under the tentorium and into the foramen magnum. They give an interesting quasi-experimental picture of the topography and at least in two instances collateral consequences of possible importance among the so-called distant symptoms of brain tumor.
The line along which the tentorium can produce depressions passes over the uncus along the subiculum of the cornu ammonis.
The case A. M., with glioma of the left opercular region, shows, beside a moderate cerebellar wedging into the foramen magnum, a characteristic sagittal "tentorial line"