Introductory Remarks

Abstract

Except for the shallow depression of the insular region, the surface of the telencephalic vesicle is still completely smooth in the fourth month of intrauterine life. The blood vessels follow quite regular courses: The arteries form a fan of rectilinear branches which dichotomize progressively. Fine branches penetrate into the parenchyma and anchor the fan to the surface. Starting in the fifth month, differential growth of the various cortical regions brings about the formation of the sulci and gyri. The vessels follow the surface and, as a sulcus deepens between two gyri, the arteries vanish into its depth as they cross it. In other words, cortical infolding deforms the previously regular vascular pattern. Arriving at the edge of a sulcus, an artery plunges to the bottom of it, rising up on the opposite lip to reappear on the free surface of the next gyrus.