The beauty of the vaulting of the central aisle is particularly noticeable when contrasted with that of the side aisles. The eastern or extended bay of the choir aisles, being new, has been vaulted with groined vaulting in the same manner as the central aisle, but the old portions of the aisles are vaulted with what nearly approaches to a domical form (Fig. 840). Each bay has the usual transverse and diagonal ribs, but the surfaces of the vault are domed up above the wall rib at the side walls, so that the height to which the windows may be carried is greatly reduced from what it might be with groined vaults, similar to those of the central aisle. The difference of this style of vaulting from the true groined vaulting used in the eastern compartment is most marked, and its effect on the height of the windows is distinctly observable in the different divisions of the aisles. [Illustration: FIG. 838.--St. Giles’ Collegiate Church. Boss in Choir.] [Illustration: FIG. 839.--St. Giles’ Collegiate Church. Cap of Vaulting Shaft in Choir.] The vaulting of the nave remained at this time unaltered at its comparatively low level, and over the vault of the central aisle there existed an attic story, which formed the house of the bell-ringer, and contained several rooms. The vaulting of the aisles of the nave (as above mentioned) had already been altered, and several chapels had been extended northwards from the north aisle. These projected beyond the old Norman porch, and thus placed it in a recess. The central crossing, with its vault, was left unaltered, and still remains in the same position, with its vaulting at the level it was raised to about 1400. It thus forms a break between the nave and choir, in both of which the vault has been raised (see Fig. 836). [Illustration: FIG. 840.--St. Giles’ Collegiate Church. South Aisle of Choir.] 3. The transepts were extended, their original length being marked by breaks in the roof, where the vaulting terminates. The extension is [Illustration: FIG. 841.--St. Giles’ Collegiate Church. Junction of Vault of South Transept.]