 In contrast, the non-parenchymal blood vessels present in the subarachnoid space are not covered by the glia limitans.Instead, the entire subarachnoid space is sealed towards the nervous tissue by the glia limitans superficialis.These two parts of the glia limitans are continuous; however, convention dictates that the part that covers the surface of the brain is referred to as the superficialis, and the part that encloses the blood vessels within the brain is called the perivascularis.