contributes to morphology of fourth ventricle fourth ventricle median aperture median aperture foramen of Majendie NCIT:C32626 arachnoid forament UBERON:0003991 neuronames:641 fourth ventricle median aperture median aperture of fourth ventricle FMA:75015 The large midline opening of the posterior inferior part of the roof of the fourth ventricle that connects the fourth ventricle to the posterior cerebromedullary cistern and the spinal cord. BAMS:MAP Wikipedia:Median_aperture MA:0002947 SCTID:279449001 foramen of Magendie BAMS:MA4V fourth ventricle aperture