with its vaulting at the level it was raised to about 1400. It forms a break between the nave and the choir, in both of which the vault has been raised.[263] (3) The transepts were extended, their original length being marked by breaks in the roof, where the vaulting terminates. In a charter dated 11th January 1454-1455,[264] it is narrated that William Preston of Gourtoun, after much trouble and expense abroad, and aided by "a high and mighty prince, the King of France, and many other Lords of France," had succeeded in obtaining an arm bone of the patron saint, which he generously bequeathed to the church. The Town Council were so gratified with the gift that they resolved to add an aisle to the choir in commemoration of the event, and to place therein a tablet of brass recording the bounty of the donor. This aisle was to be built within six or seven years "furth frae our Lady isle, quhair the said William lyis." It thus appears that the south aisle of the nave was known as the lady chapel, and that Sir William was buried there. The resolution was carried into effect, and a new aisle called the Preston Aisle was constructed, south of the lady chapel. The Preston Aisle was afterwards known as the Assembly Aisle. In carrying out the work the south wall opposite the three westmost bays of the choir was removed, and three arches carried on two piers substituted. These piers and arches correspond with the work of the same period at the east end of the choir. One of the caps contains a shield bearing the three unicorns' heads of the Prestons. The structure extends into the choir the great width of the four aisles of the church previously formed in the nave, and adds greatly both to spaciousness and grandeur. The church was now complete in all its parts, as, internally, it still remains, with a few exceptions, to the present day.[265] Several additional chapels were afterwards thrown out. In 1513 an aisle of two arches was formed by Alexander Lauder of Blyth, Provost of the city; in 1518 the altar of the Holy Blood was erected in this aisle, which lay on the south of the nave, and to the east of the south porch, immediately adjoining the south transept. It opened into the south chapels of the nave with two arches, and had two windows to the south. There was within it a handsome monument containing a recumbent statue, or forming, as some suppose, part of the altar canopy. The monument is still preserved, but one half of the chapel was obliterated in 1829.