The brain was known to have 3 protective layers containing brainal and spinal fluid, but now a fourth much thinner layer was discovered. The new layer got the name Subarachnoidal Lymphatic-like Membrane, it is only two-cell thick and divides the subarachnoid space into an upper and lower part.
Photo by: https://www.flickr.com/photos/flamephoenix1991/8376271918
