The width, too, of the jambs of doorways is often increased, and more space gained for enrichment, by giving to each order in the jamb a larger space than would otherwise be necessary of square face between the shafts (Fig. 309). [Illustration: Fig. 309. Fig. 310. Fig. 311.] In some cases, also (as in the doorway in the Castle at Durham), there is a small arch-order which continues down the jambs between the principal orders, and adds much richness to the effect. In later examples, two ranges of shafts were often introduced; the outer ones carrying the orders, and the inner ones having capitals lost under the main capitals, as if carrying an imaginary order hidden within the visible mass of the arch. These are, in fact, the parallels of the supernumerary shafts I have mentioned as often existing in clustered piers. Thus, in St. Leonard’s Priory, Stamford (a work of the twelfth century), we find two ranges backed by a plain splayed surface (Fig. 312). In the Galilee at Ely (somewhat later), the second range is backed by large hollows between salient mouldings (Fig. 310); and again at Lichfield, the back range is, as at Stamford, placed against a splayed surface, but relieved by ranges of large toothed ornaments running up behind each of the front shafts (Fig. 311). [Illustration: 312.--St. Leonard’s Priory, Stamford.] The windows also differ from mere arched openings in having a _functional_ plane, which occupies one order, and is needed to receive the glazing. The orders are never so numerous in windows as in rich doorways, rarely exceeding two besides that which receives the glass. The inner side is usually splayed, to diffuse the light through the interior. It is not my intention in this lecture to treat in detail either of doorways or windows; but having stated that a system of receding arch-orders was originally the origin of window tracery, I will say a few words in explanation of my statement.