Intercellular relationships in the external glial limiting membrane of the neocortex of the cat and rat.

The external glial limiting membrane of the cerebral cortex appears to be a complete astrocytic mantle covering the pial surface of the molecular layer. It consists of flattened cell bodies arranged singly or in small groups spaced about 100 mu apart and multitudes of interdigitating processes arrayed in layers. The glial mantle is thicker in the sulci than on the gyri. It is covered externally by a basal lamina which is associated with collagenous fibrils and cells of the pia mater. The extracellular space in aldehyde-perfused material appears as a regular, electron-lucent interval 150 A wide between adjacent cell membranes. Gap junctions are frequently encountered in the external glial limiting membrane; desmosomes are present between astrocytic processes but are seen much less often.