[Ultrastructure of the cerebral meninges]

Ultrastruct of the dog arachnoid membrane, pia (vascular) mater, internal layer of the dura mater, human arachnoid membrane, subarachnoid alveolar walls and canals transporting liquor into the subarachnoid space have been studied. From the literature analysed and from his own data the author considers the system of the meninges and intermeningeal spaces as a system of extracerebral barriers devided into 3 stdructural-functional groups: 1--barriers dealing with liquor outflow from the subarachnoid space into the blood stream (lgb-I lgb-II); 2--barriers dealing with metabolic processes between the liquor and the borderline tissues (lcb, lmb, lnb, etc.); 3--histo-haematic barriers between blood and tissue elements of the pia mater, dura mater and paravasal nerve trunks of the brain magistral arteries. Morphological substrates of some extracerebral barriers are described at a submicroscopical level.