The triforium design consists of large segmental arches, the same width as the main arches, springing from short clustered piers introduced between them. It somewhat resembles the triforium of the nave at Dunkeld Cathedral. The clerestory is probably designed in imitation of that of Glasgow Cathedral, and is divided into two pointed arches in each bay. They spring from a series of clustered shafts with round moulded caps that are late imitations of early work.[395] The earlier part of the nave restoration, including the main piers and arches, and perhaps the tracery of the two lower windows of the west front, were possibly executed by Bishop Lithgow, who built the north porch, and the completion of the nave (the upper portions) was carried out in the time of Abbot Tervas--the middle of the fifteenth century. A peculiarity of the nave interior is a series of large corbels, which project from the spandrils of the triforium arcade, and the object of which was to enable a passage to be carried round the solid piers introduced between the windows. Each of the large corbels springs at its lowest point from the sculptured grotesque figure of a man or animal. They were mostly the work of Thomas Hector, a sculptor, who lived at Crossflat,[396] and whom the abbot retained for his skill in the art.[397] The employment of such grotesque figures was very much affected by the monks of Clugny, and was the occasion of a rebuke from St. Bernard. "What business had these devils and monstrosities in Christian churches, taking off the attention of the monks from their prayers." One of these figures near the west gable represents a man in a kilt, and Dr. Lees thinks that many worshippers in the Abbey in more modern times have in the midst of long sermons found relief in the contemplation of those curious carvings which the saint thus vigorously denounced.[398]