The Subdural Space and Its Linings

Since the monumental work of Key and Retzius¹it has been generally accepted that the subdural space is lined by endothelium (mesothelium), as are the serous spaces. Mallory,²in 1920, asserted that the subdural space is not lined by endothelium, but by fibroblasts, the cells lining the dura being highly differentiated fibroblasts and those covering the arachnoid, less highly differentiated fibroblasts. His findings, however, have not influenced histologists or neuropathologists, even though Harvey and his associates³have called attention to the differences in origin and reaction of the dura and the pia-arachnoid. Lear and Harvey3econcluded from experimental evidence that the dura is lined by mesothelium derived from the mesenchyme, while the lining (covering) of the arachnoid is made up of cells more highly differentiated than those of the dura, and therefore more stable in character. In a study of subdural hemorrhages the great differences between