The space located between the dura mater and arachnoid layer.
                                                            
                                                     
                        
                                                
                        
                        
                            a space between the dura mater and the arachnoid of the brain and spinal cord; it contains a small amount of fluid
                                                            
                                                     
                        
                                                
                        
                        
                            The space located between the innermost layer of the dura mater and the arachnoid mater. This is often the area of rupture of delicate thin-walled veins following head injuries.