The columns of the choir arches have been modernized, and there is consequently but little of the old structure visible on the inside, the Retablo rising to the groining, and concealing the arches of the apse. Between these arches sculptures in stone are introduced, which are said to have been executed by Juan de Borgoña, in 1540. They are bold and spirited compositions in high relief, and give great richness of effect to the aisle towards which they face. The subjects are--(1) the Agony in the Garden; (2) our Lord bearing His Cross; (3) the Crucifixion; (4) the Descent from the Cross and the Resurrection; (5) the Ascension. Numbers 1 and 5 are not original, or at any rate are inferior to and different in style from the others. When we leave the choir for its aisles, we shall find that everything here, too, has been more or less altered. Chapels of all sizes and shapes have been contrived, either by addition to or alteration of the original ground-plan; and, picturesque as the _tout ensemble_ is, with dark shadows crossed here and there by bright rays of light from the side windows, with here a domed Renaissance chapel, there one of the fourteenth century, and here, again, one of the fifteenth, it has lost all that simplicity, unity, and harmony which in a perfect building ought to mark this, the most important part of a church. In truth hardly any part of the aisles or chapels of the chevet of Bishop Maurice now remains; for of the two early chapels on the north side (marked _a_ and _b_ on the plan), the former is evidently of later date, being possibly the work of Bishop Juan de Villahoz, who founded a chapel here, dedicated to S. Martin, in A.D. 1268-69.[16] The style of this chapel is very good middle-pointed; the abaci of the capitals are square, the tracery is geometrical, the vaulting very domical, and its north-western angle is arched across, and groined with a small tripartite vault, in order to bring the main vault into the required polygonal form. This arrangement occurs at an earlier date, as I shall have presently to show, at Las Huelgas (close to Burgos), but ought to be noticed here, as the same feature is seen reproduced, more or less, in many Spanish works of the fifteenth century, and here we have an intermediate example to illustrate its gradual growth. It is, in fact, the Gothic substitute for a pendentive.