With the growth of the developing embryonic brain, increasing requirements for oxygen and metabolic substrates demand a more comprehensive and complex vascular system. Covering the entire neuraxis is a primitive network of mesenchymal cells known as the meninx primitiva. The meninx follows the folds that appear during development of the brain, filling the interhemispheric fissure that forms between the two lateral telencephalic bulges to ultimately become the falx cerebri. At this early stage (embryo < 4 mm length), there is no differentiation into arteries and veins; the irregular network of endothelial vascular channels constitutes a primitive germinal bed of endothelium rather than a true circulatory system. The meninx primitiva differentiates into three discreet layers, which will ultimately become the dura mater, the arachnoid, and the pia mater [7]. Ultimately, angioblastic cells from the meninx become applied to the superficial surface of the developing brain, then penetrate the surface and extend perpendicularly to the pial surface between the glial elements, forming an extensive capillary-like network of endothelial cells (endothelial “buds”) [2, 7-9].