_e_, Second foot-hook, from 6 to 10 feet long, and from 6 to 13 inches deep, thickness 1/6th less than depth. This curve, when of great size, is valuable as, breast-hooks—curved timbers stretching horizontally within and at right angles to the bow-timbers, to support the bow. _f_, _f_, _f_, Knees, the one wing nearly at right angles to the other; from 2 to 9 feet in length of wing; depth at middle as much as possible; thickness from 4 to 12 inches,—generally required about 3 1/2 feet in length of wing, and from 6 to 8 inches thick. Knees, when large, suit for high rising floors. Fig. _h_ is a valuable piece, and easily procured by bending the young plant; when cut, it forms two second foot-hooks. Figs. _a_, _b_, _c_, _d_, _e_, are suitable, though the part cut off by the dotted line be awanting. In good work, this plan is often followed, and a cross-chock put on. (Vid. _s_, left side of the cross-section of a vessel thus timbered, page 20). By this {19} mode of building, vessels can be constructed from much straighter timber, and the vessels are superior, from being more elastic; but from the nicety and expense of the work and waste of timber, the practice is not much in use. {20}] [Illustration: Cross-section of a Vessel at midships—knees not inserted.] A first foot-hook alternates with each floor, and second foot-hook, alongside, extending from _o_ to _q_; and a top-timber, or third foot-hook, alternates alongside of each second foot-hook, and chock extending from _q_ to _a_. These timbers are bolted together, and constitute a frame or double rib; and the skeleton is composed of a series of double ribs (several inches separate, of course wider above than lower down, as the timbers decrease in thickness), to within a little of the bow and stern, where the timbers are usually placed singly, without framing. {21} In large vessels a fourth futtock is used; thence straighter timber is suitable. The knees occupy the position at _x_, stretching horizontally along the inside of the vessel and end of the beams. Of British trees, timbers are formed of oak, Spanish chestnut, larch, red-wood pine, red-wood willow (the stags-head ozier, _Salix fragilis_), and sometimes the broad-leafed elm (_Ulmus montana_) under water. In Britain, crooked oak for timbers is found chiefly in hedge-rows and open forests, where the winds, casual injury, or overhanging superior branches, have thrown the tree, while young, from its natural balance; or, by the tree, from open situation, or excision of lower branches, parting early into several leaders, which, in receding from each other, form curves and angular bends. On the Continent of Europe, in the natural forest, it is chiefly the tops of old lofty trees which afford the crooks; in consequence, those we import are, for the most part, of a free, light, insufficient quality[9]. {22}