Brain lacks lymphatic system so CSF acts as a partial substitute. Dura mater is a tough, shielding connective tissue firmly attached to the skull and includes the subarachnoid space filled with the CSF, arteries and web-like connective tissue called archanoid mater. The pia mater is a completely sensitive and permeable membrane composed of collagen, elastin and fibroblasts that rests on the ground of subarachnoid space and lets in diffusion between CSF and the interstitial fluid of mind tissue.