The ceremony of the Mass contained portions that were unvarying; other elements changed to accommodate prayers for special intentions, the commemoration of a local saint, a funeral, or celebration of a great feast such as Easter.  The high altar in Notre-Dame of Paris was constructed with a screen for fabric hangings between statues of angels holding instruments of the passion. The hangings could be changed according to the nature of the ritual and season of the year.  A few of the statues from the enclosure are still extant.  (Viollet-le-Duc, Architecture, 2:30: Paris, Notre Dame) back to "worship"