A spiral thickening of the fibrous lining of the cochlear wall. Spiral ligament secures the membranous cochlear duct to the bony spiral canal of the cochlea. Its spiral ligament fibrocytes function in conjunction with the stria vascularis to mediate cochlear ion homeostasis. [ https://github.com/obophenotype/mouse-anatomy-ontology/issues/71 http://en.wikipedia.org/wiki/Spiral_ligament ]