[Illustration: Fig. 162.] [Illustration: Figs. 163, 164.] and in subsequent styles, a special variety of internal arch is introduced suited to those numerous cases in which the glass-plane is far nearer (as it is in a majority of instances) to the outer than the inner face of the walls. The simplest form of this internal window-arch takes the form of a barrel (pointed) arch, springing so much lower than the spring of the outside arch as to allow it to span the increased internal width without rising unduly higher than the outside arch, as was the case when the splay was continued round the inner arch. This arch of necessity formed an intersection with the inside splays. Its edge was usually in the plainest specimens, relieved by a chamfer (Fig. 159), which was often exchanged for a moulding (Fig. 160); but a far more agreeable finish was a rib dropping down a little from the arched soffite, its edges being either chamfered or moulded with or without a label over it (Fig. 161). This, if the arch were made slightly segmental, would die into the jamb-splay, or it might be carried on a corbel (Fig. 162) or a shaft (Figs. 163, 164), thus forming a very agreeable and picturesque internal finish to the window. This rib is usually termed a rere-arch. Professor Willis, in his paper on the _Architectural Nomenclature of the Middle Ages_, calls it a “Scoinson Arch,” from a French word “_escoinsons_.” He also quotes the term “_arrière voussure_,” probably meaning the arch behind the rib. Professor Willis’s general description, which I had not referred to when I wrote the above, is as follows:--“An arch is placed so as to carry the inner surface of the wall. In simple examples, like the present, this rib is plain, and dies against the jambs, but in superior buildings is richly moulded, and a shaft, with base and capital and side-mouldings, are added to the edges of the jamb. But this arrangement is mostly distinct from the window-tracery. This arch is of different and larger span from that of the window-head, because the spreading or embrasure of the jambs increases the opening inwards. It is also of a different curvature, and the decoration of the two disconnected and separated by the plain splayed sides of the window-opening, connecting the two, and resting at one end on the tracery, and at the other on the rib, is a narrow vault or _voussure_, which again is not necessarily of the same curvature as the sustaining arches, but which carries the core of the wall above.”