The ependyma is a simple ciliated epithelium that lines the ventricular surface of the central nervous system, extending from the lateral ventricles to the filum terminale. In some publications, the term is used somewhat inaccurately to include all tissues lining the ventricles; I will use the term very strictly as defined above. Mature ependymal cells
appear along the neural tube as the ventricular zone regresses [21], the timing of which is location and species dependent. In humans, the ependymal lining is complete by approximately 26–28 weeks gestation. Mature ependymal cells are characterized morphologically by a cuboidal to columnar shape and a fairly round nucleus with fine stippled
chromatin pattern and inconspicuous nucleolus. The surface is covered by microvilli and most of the cells have a central cluster of long cilia. The closely apposed lateral margins tend to be nearly perpendicular to the wall of the ventricle and are joined near the apical surface by zonula adherens type junctions. Between the basal surface of the ependyma and the underlying web of astroglial process exists a basement membrane that is demonstrable only with special staining methods. On the surface of the ependymal layer is a network of supraependymal axons (Fig. 1).