inferior medullary velum inferior medullary velum 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 the infero-posterior part of the fourth ventricle. inferior medullary velumscheme of roof of fourth ventricle. the arrow is in the foramen of majendie.1: inferior medullary velum2: choroid plexus 3: cerebellomedullary cistern of subarachnoid cavity4: central canal5: corpora quadrigemina6: cerebral peduncle7: superior medullary velum8: ependymal lining of ventricle9: pontine cistern of subarachnoid cavitydetailsidentifierslatinvelum medullare inferiusneuronames697anatomical terms of neuroanatomy 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 taeniae.