There are also sixteen small stone heads, four connected with each group of three Apostles, which are not very clearly seen, perhaps, from the floor of the Cathedral, but which, when examined, shew by the conventual prophetic cap given to them, that they are intended to represent the sixteen Prophets of the Old Testament. Above these canopies, in each of the four sides, is a gallery or passage with an embattled parapet, and above that a large window of four lights with geometrical tracery; it is extremely sharp pointed, and towards the top each window is faced internally with a trellis or lattice-work of stone, which adds to its elegance without intercepting the light. These windows rise to the same height as the higher arches; they have been filled with stained glass by Mr. Wailes, and the subjects are chiefly representations of persons who were instrumental in the foundation, erection, or restoration of the Cathedral, of the reigning sovereigns at the respective periods, and of others who figured in the traditionary history of the foundress. The window in the south-east angle is designed to commemorate the principal persons who figured in the traditionary history of the foundress. The figures in the upper tier represent Anna, father of St. Etheldreda; St. Etheldreda as queen; Tonbert, her first, and Egfrid, her second husband. In the lower tier, St. Etheldreda as abbess; Wilfred Bishop of York; St. Erminilda, the third abbess; and St. Sexburga, the second abbess. The tracery contains other figures and emblems, with the arms of the donor, the late Canon E.B. Sparke. The window in the north-east angle, in continuation of the same design, contains in the upper tier figures representing St. Withburga, St. Edmond, St. Werberga, fourth abbess of Ely, and Archbishop Dunstan. In the lower tier, Bishop Ethelwold; Brithnoth, Duke of Northumberland; Abbot Brithnoth, and King Edgar. The tracery contains the arms of the University of Cambridge, with other figures and devices: contributed by subscriptions from the Bachelors and Undergraduates of the University of Cambridge.