modifications were, consequent upon the change that was wrought in the profiles of the archivolts and vault ribs from the square to the polygonal section.
Arch sections of other than square form had sometimes been employed from the earliest times. But these forms, as we shall presently see, were very simple and did not lead
FIG. 119.
to any change in the form of the abacus. But now that more complicated mouldings were being introduced, and the arch section was becoming polygonal in its general outlines, the form of the abacus was made to correspond with it. The bell remained substantially unchanged, but the absence of the far-projecting angles of the abacus removed the reason for the supporting crockets, and though crockets continued to be introduced, they now became more orna-
