Between the skull and the brain, we knew so far three membranes, or meninges. A fourth has just been added, which is literally part of the waste disposal system.
Called SLYM (subarachnoid lymphatic-like membrane), this membrane is very thin — hence the pun with slim, or thin in English). It is barely a few cells thick in some places.
It is located in the subarachnoid spacewhich separates two of these membranes, called arachnoid and pia mater.
Membrane presque invisible
It is too thin to be detected by modern technologies that can observe brain activity from the outside. And it disintegrates when the brain is removed from the skull during an autopsy.
