Abstract
Valves were observed in the muscular cerebral arteries of the rat at the level of the optic chiasm in each of the ten adult animals examined. These paired valves were formed by folds of the intima. They were frequently associated with a branching of the artery. Part of the well formed internal elastic membrane separated the base of the valve from the media, while some very thin elastic fibers spread through the tissue forming the valve. The area of the valve was stained metachromatically by cresyl violet and was sharply differentiated from the remaining non‐metachromatic arterial wall. The internal elastic membrane was intensely stained by fuchsin paraldehyde, PAS, orcein and silver diammine.