A thin, transparent membrane, lying immediately over the brain and The main nerve trunk running down the spinal canal and connecting the individual’s mind and consciousness to the rest of his or her body. It is about the size of a person’s little finger, in diameter. It cannot repair itself if damaged., and in turn being surrounded by This is the outer, most prominent and the toughest of the three different membranes that invest the brain and spinal cord. It also forms the lining of the cranial cavity and the spinal canal. Looked at as a whole, the dura can be envisaged as a balloon with a long sausage skin hanging below it. Within the dura the brain and spinal cord are bathed in cerebrospinal fluid.. The arachnoid forms thin membranes and strands likened by early anatomists to a spider’s web. Hence its name, referring to spiders, as in “arachnophobia”, which means the fear of spiders.