perfected there is no attempt to stilt the wall rib, but the masonry of the vault is actually curved outward from the very springing of the radiants, which are raised to the impost of the window heads to give the vault this form.[364] The highly stilted wall intersection with the consequent elevation of the clerestory window and flattening of the lower part of the vault cell constitutes the great structural advance in the chevet of Saint Germer. The employment of the wall rib, however, introduces an important matter for discussion. To be sure this is not by any means the first example of its use, for formerets may be found even in groined vaults, but it is one of the early examples on a large scale and may serve to introduce the question as to the part which these ribs played in Gothic architecture. THE USE OF WALL RIBS IN GOTHIC RIBBED VAULTING It has generally been maintained that the wall ribs were integral and important members of a true ribbed vault and that they actually aided in the support of the masonry panels. There are, however, a number of reasons for believing that this is not entirely so but that these ribs were comparatively unimportant as far as their relation to the vaults was concerned and were of much more importance, in the first place as cover joints, in the second as window heads, and in the third as relieving arches in the clerestory wall. Two important facts lend strength to the theory that the wall rib was not as a rule a supporting member. The first of these lies in the fact that it was quite frequently omitted even from vaults of the true Gothic form, and the second, in the fact that, when present, there are perhaps as many cases in which the curve of the vault fails to follow that of the rib as there are of the reverse condition. In fact, it is a question whether in the majority of cases the vault panel actually rests upon or even cuts into the face of the formeret. Take, for example, a number of chevet vaults[365] and examine them in this respect. At Saint Germer (Fig. 63) the wall rib is largely a relieving arch in the clerestory wall which is made much thinner beneath it; and while the curve of the chevet cells follows in general that of the arch, it does not exactly correspond with it. In the large chevet vault of Saint Remi at Reims (Fig. 64), and in many other vaults not over the apse, especially in the English churches and those in which a group of clerestory windows is found in each bay, no wall rib is used, showing that such a rib was not at all necessary as far as the construction and support of the vault was concerned. Moreover, in many of the churches in which a wall rib is used along the exact line of the vault surface, it is too small to act as a supporting member and would seem to be merely a cover-joint to hide the intersection of the vault surface with the clerestory wall.[366] Finally and most important of all are the cases in which this rib is used primarily as a window head. In