Dr. William G. Spiller, in an article1 entitled "Cranial Hyperostosis Associated with Underlying Meningeal Fibroblastoma," discussed the invasion of the bones of the skull over a fibroblastic tumor, the condition having been described by him originally in 1899. It is known that thickening of the bones of the vault is a not unusual accompaniment of an underlying fibroblastoma, and the appearance is characteristic in the x-ray film. Penfield, quoted by Spiller, stated that enlargement of the bones at the base of the skull from tumor infiltration in association with adjacent endothelioma would be of diagnostic importance in regard to the question of the origin of the bony enlargement. Spiller made the important observation that, as far as he knew, "in no case of fibroblastoma at the base of the skull has infiltration of the bone by the tumor been described." It was thought by both Spiller and Penfield that