The lower church (see Fig. 571), supporting as it does the choir with its aisles and the east aisle with its chapels above, conforms in its structural arrangements to the plan of the upper church. Thus all the pillars in the simpler plan above are supported by pillars in the more complicated plan below. In the latter, between each of the main piers of the arcade, lesser piers are introduced; so that while there are four pillars and five bays on each side of the choir above, there are nine pillars and ten bays in the church beneath. The central area of the lower church is further subdivided by a simple and beautiful scheme of pillars and vaulting, which is arranged in the following manner (Fig. 578). A central shrine of four slender pillars (Fig. 579) is placed opposite the sixth bay, counting from the eastern aisle, and is situated under the high altar of the choir. This shrine is made the centre of the scheme for the vaulting of three bays on each side; the remaining bays on the east and west being treated so as to form a variety both in the piers and vaults. From the shrine as a centre a single central pillar is introduced in the spaces to the east and west, and in the bays beyond them two pillars are introduced in the breadth, and the vaulting is varied so as to suit this arrangement of the pillars (Figs. 580 and 581). The vaulting of the lower church is a masterpiece of design, and produces by very simple means a wonderful variety of effect. It is analysed by Sir G. Gilbert Scott in his lectures, and greatly commended. This vault has been the subject of very careful examination by Mr. T. L. Watson, architect, Glasgow, who points out that it must have been erected at a later period than the rest of the choir. This he proves from the mouldings, which are of a later character than those of the choir. His view is that the original intention was to vault the central aisle with a series of cross vaults similar to those in the side aisles, and he points out that the springers for these vaults were built along with the piers. The central vault, however, was delayed for convenience of building operations till after the upper portions of the choir were finished, and, when this vault came to be executed, the architect had devised the more beautiful scheme which is actually carried out. This required some alteration of the springers, and Mr. Watson draws attention to the points where the alterations are visible. He also points out that the two central east windows of the lower church are different from the others (see Fig. 568). The latter are all double lancets, whereas the former have each one large arch enclosing two smaller ones. The larger arches would be left open during the progress of the work for the introduction of building materials, and the filling in of the smaller arches would be done after the building was completed. [Illustration: FIG. 578.--St. Mungo’s Cathedral. Plan of Lower Church, showing the Vaulting.]