The contributing elements to boundaries of the round window niche are superiorly the tegmen fossula fenestra rotunda (roof support), inferiorly the fustis (depth) and area concamerata, anteriorly the sustentaculum (support) and postis anterior (anterior pillar), and posteriorly the postis posterior (posterior pillar) and the subiculum (underlying supporting structure). Variations in their size and orientation can give rise to significant variability in the overall size and shape of the round window niche.
