a double fold of pia mater, enclosing subarachnoid trabeculae, between the fornix above and the epithelial roof of the third ventricle and the thalami below; at each lateral margin is a vascular fringe projecting into the choroidal fissure of the lateral ventricle; on its undersurface are several small vascular projections filling the folds of the ependymal roof of the third ventricle. SYN: tela choroidea ventriculi tertii [TA], tela choroidea superior, triangular lamella, velum interpositum, velum triangulare.