deposits of beta-amyloid also form in the walls (in the "tunica media", the middle layer, and "tunica adventitia" or "tunica externa", the outer layer) of small and mid-sized arteries (and sometimes veins) in the cerebral cortex and the "leptomeninges" (the "leptomeninges" are the two inner layers - pia mater and arachnoid - of the "meninges", a protective 3-layer membrane covering the brain.)