The neuroanatomic study of the callosomarginal artery was performed bv simple and careful dissection in 52 human brains. The observation was made with stereoscopic magnifying glass. The results were the following: the callosomarginal artery was present in 36.6% (19/52) of the cases on the right hemisphere and 29%(15/52) on the left hemisphere; unilateral absence on those hemispheres was of 17.3%(9/52) and 25.0%(13/52), respectively; bilateral absence was of 46.1% (24/52). The register of the presence or absence of the artery was based on proposed criteria by Moscow and col.14. With regard to phyllogenetic signification one has considered the hypothesis that the development of the callosomarginal artery possibly was closely related with a structural and physiological expansion of the neocortex in man.