Ependymal cells are arranged in single-palisade arrays and line the ventricles of the brain and central canal of the spinal cord. They are usually ciliated, their cilia extending into the ventricular cavity. Their fine structure has been elucidated by Brightman and Palay [38]. They possess several features that clearly differentiate them from any other CNS cell. The cilia emerge from the apical pole of the cell, where they are attached to a blepharoplast, the basal body (Fig. 1-17), which is anchored in the cytoplasm by means of ciliary rootlets and a basal foot. The basal foot is the contractile component that determines the direction of the ciliary beat. Like all flagellar structures, the cilium contains the common microtubule arrangement of nine peripheral pairs around a central doublet (Fig. 1-17). In the vicinity of the basal body, the arrangement is one of nine triplets; at the tip of each cilium, the pattern is one of haphazardly organized single tubules.