St. Mirin’s Aisle (Fig. 965), as already pointed out, occupies the south end of the south transept, and was erected in 1499. It is a chapel 48 feet 3 inches long by 23 feet wide, having a vaulted roof about 32 feet 6 inches high. The main vault, like that of so many structures of the latter part of the fifteenth century, consists of a pointed barrel vault, the curve of which is drawn from a point lower than the springing of the arch, and thus forms an angle at the junction with the side walls. The surface of the vault is strengthened with a series of ribs, most of which spring from corbels in the side walls. The ribs are arranged so as to cross one another at the ridge, as if the roof were [Illustration: FIG. 965.--Paisley Abbey. St. Mirin’s Chapel, looking East.] groined; but they are almost entirely ornamental. The mouldings of the corbels are well designed, and show an imitation of first pointed work. The corbels being at a lower level than the top of the wall, the ribs project considerably in passing that point. The ridge has a bold rib enriched with carved bosses, and one of the transverse ribs is divided into two branches, so as to avoid descending on the top of the large arch in the north wall. There is a large pointed window in the east end, having jambs with single shafts (like the clerestory of the church). It has mullions dividing it into four lights, and the arch-head is filled with good simple tracery. Beneath this window runs a frieze 1 foot 8 inches broad, partly carved, with groups of figures showing, as discovered by Dr. Lees,[14] events in the life of St. Mirin. The east end of the chapel, where the altar stood, is raised four steps above the western part. The west wall contains an outer doorway from the cloister court, and there is a window with simple tracery above it; a curious large ambry adjoins the door in the outer wall. The chapel was connected with the south transept by two wide archways, now built up. There is a piscina near the east end (Fig. 966), with three-sided head, like that in the choir.