Angles measured when determining ciliary beat pattern. A horizontal line was drawn along the ependymal edge and a vertical line drawn through the cilium at the start of the power stroke in the midline position. Frame by frame analysis allowed the precise beat pattern to be viewed. The diagram illustrates the maximum deviation of the cilium during the power stroke (light blue cilium) and the maximum deviation of the cilium during the recovery stroke (light green cilium). The following angles were measured: OL: Outer Left: angle between the horizontal and the maximum displacement of the cilium to the left of midline. L: angle of maximum deviation of cilium left of midline. R: angle of maximum of cilium right of midline. OR: Outer Right: angle between the horizontal and the maximum displacement of the cilium to the right of midline.