GROIN RIB, and also GROINED VAULTING.) The earliest groining had no ribs. In early Norman times plain flat arches crossed each other, forming Ogive Ribs. These by . degrees became narrower, had greater projection, and were chamfered. In later Norman work the ribs were often formed of a large roll placed upon the-flat band, and then of two rolls side by side, with a smaller roll or a fillet between them, much like the lower member. Sometimes they are enriched with zigzags and other Norman decorations, and about this time bosses became of very general use. (See Boss.) As styles progressed, the mouldings were more undercut, richer and more elaborate, and had the dog-tooth or ball-flower or other characteristic ornament in the hollows. In all instances the mouldings are of similar contours• to those of arches, Sze., of the respective periods. (See MouLDINGs.) lu Perpendicular work the ribs are broader and shallower, and almost always have two great hollows of elliptic shape, one on each side. In those churches of the Early English and Decorated periods where there is a groining of wooden ribs filled in between the spandrils With their narrow oak boards, these ribs resemble those of stone, but are slighter, and the mouldings not so bold. (Sec CEILING.) Later, wooden roofs are often formed into cants or polygonal barrel vaults, and in these the ribs are generally a . cluster of rounds, and form square or stellar panels, with carved bosses or shields at the intersections..