WITH 16 FIGURES, 12 CHAETS, AND 7 TABLES.From time to time in the past hundred years attempts have been made to determine the distinctive points of difference between the Caucasian and the Negro brain. While differences in skull capacity, in brain weight and size-especially of the frontal lobes-or in the gyri have been demonstrated by Gratiolet, Tiedemann, Broca, Manouvrier, Peacock, Marshall, Parker, and others,-more recently 1, s Waldeyer in Germany and by Elliott Smith in Egypt,-yet no exact measurements of the brain, such as we have of the skull, are to be found.' An effort will be made to show by measurement of outline drawings of brains in different positions, by composites of these outlines, and by actual drawings from individual brains that there is a difference in the size and shape of Caucasian and Negro brains, there being a depression of the anterior association center and a relative bulging of the posterior association center in the latter; that the genu of the corpus callosum iF: smaller in the Negro, both actually and in relation to the size of the splenium; and that the cross section area of the corpus callosum is greater in relation to brain weight in the Caucasian, while the brain weight of Kegro brains is actually less. The amount of brain matter anterior and posterior to the fissure of Roland0 is roughly estimated, but other points of possible difference, as in the gyri, the insula, the opercula, the "Affenspalte," the proportions of white and gray matter, and the cerebro-cerebellar ratio are necessarily omitted in this study.In December, 1904, I reported to the Association of American hnatomists the results of the measurements of fifty-four brains, thirty-seven from American Negroes, and seventeen from American Caucasians, Since 'The brains measured for this work are in the Wistar Institute under the same numbers given in Table I.