2. The delicate serous membrane, or membranous sac, lining the dura mater, and enveloping the brain and spinal cord.
Like a cobweb referring to a thin membrane between two other membranes surrounding the brain and the spinal cord.
Arachnoiditis is the name applied to inflammation of this membrane.
Villi are minute hairlike projections, or tiny finger-like or vascular projections, on the mucous membranes.