I wish to present here certain observations that were made in a gross and microscopic study of the dura mater removed at necropsy in fifty-nine cases in the Mayo Clinic, which, as correlated with certain clinical observations, are suggestive as to the source of endotheliomas.
The gross examination of the dura mater, stripped from the skull and handled with care, showed, in a large percentage of cases, small nodular or vesicular outgrowths, which were found often in juxta-position to the meningeal vessels, as well as in other parts of the dural surface (figs. 1 and 2). This is not a new observation. Observers1 in the middle of the last century called attention to similar peculiar cellular proliferations, the etiology and complete significance of which still retain important elements of conjecture despite more recent excellent contributions to the subject.2
Microscopically, it was found (fig. 2) that these nodular