The edifice consists (Fig. 570) of a nave of eight bays, with side aisles measuring about 122 feet in length by 61 feet 9 inches in breadth within the walls (the whole length of the edifice being of this width); transepts, which do not project beyond the aisles; a choir of five bays, with side aisles and an aisle at the east end of the same height as the north and south aisles, with chapels beyond it. Entering from one of the eastern chapels is the sacristy or vestiarium at the north-east corner of the choir. A wide staircase leads down from the crossing on each side to the lower church, or crypt, as it is usually called (Fig. 571), and from the lower church is the entrance to the chapter house, immediately below the sacristy. On the south side of the church, and in continuation of the south transept, is situated another low church or crypt, called “Blackadder’s Aisle;” and on the north side, opposite the west bay of the choir, are the foundations of what has apparently been intended to be a large chapel. Over the crossing rise the tower and spire to the height of 217 feet. The church measures about 283 feet in length by 61 feet 9 inches in breadth within the walls, and the central alley of the nave and choir measures between the pillars about 25 feet 3 inches. As already mentioned, the most ancient part of the structure, according to Mr. Honeyman, is the portion of the lower church at the south-west angle. Mr. Honeyman’s theory is that the church built by Bishop John (Achaius) was restored by Bishop Joceline at the end of the twelfth century, and that the above portion at the south-west angle formed a chapel, and was part of that restoration.[64] He supposes that this chapel, situated in a corner of the old building least likely to be interfered with by the proposed operations, had been preserved as a receptacle for relics while the choir and lower church were being rebuilt by Bishop Bondington in the thirteenth century. Mr. Honeyman points out that one shaft and cap in the east wall of the above chapel and part of the wall adjoining, into which the shaft-stones are bonded, are of the transition style, and correspond with some other fragments of the same style which have been discovered lying loose, and which all appear to have been part of the work carried out in Bishop Joceline’s time. The vaulting of this south-west chapel is also of transition character; but from other indications it is thought that this vault has probably been rebuilt with old materials. These indications are that the shafts, with [Illustration: FIG. 569.--St. Mungo’s Cathedral. View from West.] [Illustration: FIG. 570.--St. Mungo’s Cathedral. Plan of Nave and Choir.] [Illustration: FIG. 571.--St. Mungo’s Cathedral. Plan of Lower Church.]