In the south-west angle of the church is the interesting Mozárabic Chapel, built in 1504 by Enrique de Egas, under the orders of the famous Cardinal Ximenes de Cisneros. It is devoted to the celebration of Mass and the offices of the church according to the Mozárabic ritual, which till the middle of the last century was followed in six of the parish churches. The Cupola dates from 1626, and was the work of Jorge Manuel Theotocopuli. The porch is Gothic, and the reja in good Renaissance style, executed by Juan Frances in 1524. The frescoes, of no great value, painted by Juan de Borgoña, represent the expedition against Oran, in which the great Cardinal took part. Miss Hannah Lynch gives a vigorously worded account of a service in this chapel according to its peculiar rite: “The quaint old ritual may be heard every morning at 9 A.M., and will be found extremely puzzling to follow. The canons, in a sombre, flat monotone, chant responses to the officiating priest at the altar. The sound combines the enervating effect of the hum of wings, whirr of looms, wooden thud of pedals, the boom and rush of immense wings circling round and round. After the first stupefaction, I have never heard anything more calculated to produce headache, nervous irritation, or the contrary soporific effect. In summer, it must be terrible.” At the opposite, or north-west, angle of the church is the Chapel of San Juan or of the Canons, so called because Mass can be celebrated here only by those dignitaries. It was built in 1537 by Covarrubias in the Renaissance style, and occupies the site of the old tower chapel, called the Quo Vadis. The ceiling is of artesonado, in gold and black, with carved flowers and figures. Since 1870 this chapel has been the repository of the Cathedral Treasure, styled Las Alhajas, or the Jewels. Here is kept the gorgeous _custodia_, or portable tabernacle, made by order of Cardinal Cisneros by Juan de Arfe, who began it in 1517 and completed it without assistance in 1524. This triumph of the silversmith’s craft is in the form of a Gothic temple, eight feet high, with all the architectural details, such as columns, arches, and vaultings, the whole resembling delicate lacework. Scenes from the life of our Saviour are illustrated in reliefs. There are no fewer than two hundred and sixty statues of various sizes, all exhibiting the same skill. The tabernacle was gilded over in 1595 by Valdivieso and Morino. The _viril_ inside, in which the Host is exposed, was made of the first gold brought from America, is completely covered with precious stones, and weighs twenty-nine pounds. In the Treasure is also included the mantle of the Virgen del Sagrario, considered by Señor de Riaño the most remarkable specimen of embroidery that exists in Spain. It is described in the following manner: “It is made of twelve yards of cloth of silver, entirely covered with gold and precious stones. In the centre is an ornament of amethysts and diamonds.