This communication will be chiefly devoted to but one of the many interesting features of the endotheliomas, namely, the hyperplasia of the adjacent bone. That the relationship between the meningeal tumor and the hyperostosis is not generally understood was brought out at a recent meeting of the Society of Neurological Surgeons held in Philadelphia. At that time Professor Spiller exhibited many interesting specimens from his extensive collection of brain tumors. In showing some examples of endotheliomas he stated that these tumors were sometimes associated with an overlying cranial hyperostosis which he considered to be the cause of the subjacent growth. This opinion was so contrary to that which has long been held and taught in the writer's clinic, that this occasion is taken to present some data bearing on this particular aspect of these lesions. It is quite probable that the true character of the bony tumor has often been