Inferior medullary velum

Overview
The inferior medullary velum (posterior medullary velum) is a thin layer of white substance, prolonged from the white center of the cerebellum, above and on either side of the nodule; it forms a part of the roof of the fourth ventricle.

Somewhat semilunar in shape, its convex edge is continuous with the white substance of the cerebellum, while its thin concave margin is apparently free; in reality, however, it is continuous with the epithelium of the ventricle, which is prolonged downward from the posterior medullary velum to the ligulæ.