Directly under the ependyma, and between the ependymal cells, there are basement membranes which form labyrinths connecting with the perivascular basement membranes of the subependymal vessels. The basement membranes exhibit differences in form, position, and distribution, and they can be distended by fluid absorption into large lacunae. The membranes can be identified as glycoprotein and glylcolipid substances. Electron microscopic studies have shown the differences between the basement membrane labyrinths of the human, the rabbit and the rat. In the human, the labyrinths contain isolated collagen fibrils. Basement membranes generally line all connective tissue spaces and form their interstitial borders. From this point of view, the subependymal basement membrane labyrinths can be seen as interstitial spaces near the ventricles, forming pathways between the ependyma and the subependymal capillaries or postcapillary veins.