part_of part of part of composed primarily of bicellular tight junction endothelial blood brain barrier arachnoid barrier layer UBERON:0000437 The arachnoid barrier layer is a part of the arachnoid meningeal layer. It is formed by tight junctions between the endothelial cells of cerebral capillaries in the arachnoid mater. BTO:0002498 FMA:231559 arachnoid mater organ component layer