Endolymphatic sac

From the posterior wall of the saccul, a canal, the ductus endolymphaticus, is given off; this duct is joined by the ductus utriculosaccularis, and then passes along the aquæductus vestibuli and ends in a blind pouch (saccus endolymphaticus) on the posterior surface of the petrous portion of the temporal bone, where it is in contact with the dura mater.