The clock was originally located on the western wall of the southern transept, above the steps to the monks dormitories.

In 1412 a small chapel was built next to the southern transept.

A stair in the southern transept leads to the dormitory, dating to 1493.

The graceful southern transept, the oldest portion of the whole edifice, terminates in an apse.

The building was widened and a southern transept was completed.

Only the southern transept and its bell-tower still exist.

Gavin Dunbar, who followed him in 1518, completed the structure by adding the two western spires and the southern transept.

From the southern transept rises the bell tower, built in the 12th-14th centuries, with a series of single, double and triple mullioned windows.

The overall effect was of an extension of the southern transept to include the chapter house.

The architect had, however, made a maquette of the original design, which is preserved in the southern transept.