THE MANY and varied concepts of defects, or agenesias, of the corpus callosum will be easily understood by a comparison of two recent papers on this subject. De Morsier and Mozer1suggested as an etiologic factor a disturbance during the closure of the anterior neuropore, as had previously been proposed by Marchand,2Goldstein3and Ernst.4De Morsier and Mozer1described a second type, in which an embryonal neoplastic agent, a lipoma or an angioma, destroys the corpus callosum (callosal body) during fetal life. Eventually, they claimed that disturbances in the vascularization of the lamina terminalis by the anterior callosal artery during fetal life was another cause. Kirschbaum,5on the contrary, suggested porencephaly as a cause of agenesia of the corpus callosum, whereby, in agreement with Yakovlev and Wadsworth,6an agenesia of the gyrus cinguli is the causative factor. In my paper presented at