The long corridor, 28, which lies to east and west of the central court and its group of chambers, turns at right angles and encloses the whole central block. The corridor is covered by a semicircular stone vault, oversailing the walls; at four points, however, it is left unroofed in order to admit light and air. These openings are flanked by transverse arches, springing a few centimetres lower than the spring of the vault. The angles of the corridor are roofed with groined vaults, and groined vaults occur in two places, towards the middle of each of the long sides of the corridor. Moreover, a small extension of the east arm of the corridor, No. 61, is also roofed with a groin. This last is the example given by Dr. Reuther on Plate 13 of _Ocheïdir_; it is the only groin in the palace which is built of brick. Where the groins do not rest on the head wall, they are laid against transverse arches, springing from a point lower than the springing of the vault. The lower parts of the groin are built of stones laid horizontally and forming a bracket from which spring the intersecting vaults (Plate 32, Fig. 2). The vaults are also built of thin slabs of stone, cut in the shape of bricks, and laid with a slight inclination backwards against the head wall or the transverse arch. This construction demanded little or no centering. In the north-east angle of the corridor there is a small door in the east wall which gave access to a stair or passage running under the wall. It was so much blocked by ruins that I could not penetrate into it.