After that of Saint Germer-de-Fly, perhaps the next important chevet is that of Saint Martin-des-Champs at Paris (Fig. 65), which dates from about 1140-1150 and may possibly be the earliest of what will be termed broken-ribbed chevets. On the exterior, this apse closely resembles Saint Germer with no flying-buttresses and only very light exterior buttress-shafts. In the interior, however, there is a marked difference between the two, for the apse of Saint Martin-des-Champs is so constructed as to include not merely the bays actually on the curve, but one rectangular bay of the choir as well. The builders thus set themselves the problem of constructing a chevet vault with seven cells, over a space greater than a semicircle. If they had made all the radiants of such a vault meet at the crown of the transverse arch, there would have been a great disparity in the length of the ribs and a very awkward shape to the separate vault cells. To avoid this, and to do away with the pressure of the radiants at the crown of the apsidal arch, the builders moved the keystone of the radiating ribs back from this crown to a point where all of them become nearly equal in length. And since the bay with parallel sides was of practically the same size as four[368] of those making up the apse proper, the keystone fell very nearly on the transverse line between the two piers marking the eastern end of this bay (Plate II-c). In none of the chevets of this type did it fall directly at the center of such a line, however, and it is this fact that differentiates the chevet vaults of broken-ribbed character from the slightly later and more developed buttressing-ribbed type. A vault like that at Saint Martin-des-Champs, marks an advance over that at Saint Germer in that the two western ribs furnish admirable abutment for the keystone of the vault, and the added choir bay gives a more spacious appearance to this portion of the church. [Illustration: FIG. 65.--PARIS, SAINT MARTIN-DES-CHAMPS.] There is another example of this broken-ribbed chevet in Paris, in the church of Saint Germain-des-Pres (cir. 1163), while still others may be [Illustration: FIG. 66.--VÉZELAY, LA MADELEINE.]