The median aperture (median aperture of fourth ventricle or foramen of Magendie) is an opening at the caudal portion of the roof of the fourth ventricle.

[1] It allows the flow of cerebrospinal fluid (CSF) from the fourth ventricle into the cisterna magna.

[4] The median aperture varies in size but accounts for most of the outflow of CSF from the fourth ventricle.

[1] The median foramen on axial images is posterior to the pons and anterior to the caudal cerebellum.

It is surrounded by the obex and gracile tubercles of the medulla, tela choroidea of the fourth ventricle and its choroid plexus, which is attached to the cerebellar vermis.