This article presents the results of an analysis of the variable and surgically important relationship between the oval window, the fossular walls and the related posterior tympanic recesses in 50 temporal bones. The visual impressions of superficial and deep oval windows seem to correspond fairly closely to the depth of the inferior wall of the fossula fenestra vestibuli (FFV). The depth of the superior and anterior walls of the FFV by themselves, did not appear to have such a dominating relationship in determining the deep oval window. There does not appear to be a well defined posterior wall in the vast majority of the specimens (86 percent). In the event of scar tissue forming between the superior, inferior and anterior walls, the gap between the postero-superior part of the promontory and the posterior tympanic wall (posterior communication) could allow aeration of the region of the deep oval window in such an instance. Closure of this gap by a solid shelf of ponticulus or scar tissue could cause a localized malaeration of the fossula in most cases of deep oval windows. This is an entirely new concept of the likely problems of malaeration of a deep oval window which could arise due to anatomical variations and of the possible safety valve mechanism which could prevent such malaeration and its consequences.