In making these grooves we must say that we think the use of the special saw may be dispensed with, and the incisions just as easily, or, at any rate, just as successfully, made with the knife. Those who select to use this instrument should choose a narrow-topped and sharp searcher, or a modern shaped drawing-knife of suitable size, such as those depicted in Fig. 46, _a_ and _b_, and they will find their work much easier if they will make the first steps in the incisions with an ordinary flat firing-iron. By the use of the latter instrument the grooves are made conveniently open along their tops, and room left for nicely finishing the more delicate manner of removing with the knife the softer horn near the sensitive structures. Those whose leaning is towards the use of special instruments, but who, at the same time, do not care to use the saw, will find their wants supplied in the hoof plane (Smith's), Fig. 146, or the hoof chisel (Hodder's), Fig. 147. With the hoof plane the groove in the wall is made by a succession of downward scraping movements, while with the chisel the cut in the wall is made either from below upwards, or from above downwards, according as the foot is held forward or backward--whichever, in fact, comes most convenient. [Illustration: FIG. 146.--HOOF PLANE (SMITH'S).] When using the knife or the hoof plane it is not often that the sensitive structures are injured. In all cases, however, no matter what the instrument used, the metal gauge should be employed when the sensitive structures have been touched, and the operation obscured by blood. [Illustration: FIG. 147.--HOOF CHISEL (HODDER'S).] Our instruments at hand, the operation may be proceeded with. The first step is to ascertain the extent of the side-bone, and to determine the position of the incisions. To do this the coronet is felt with the thumb, and the anterior extremity of the side-bone noted. This is marked on the horn with a piece of chalk, and a vertical line dropped from this position to the inferior margin of the wall (Fig. 148,1). The line crosses the horn fibres obliquely, and is purposely made in that direction in order that its inferior end may be far enough back to avoid the last nail-hole. Should the side-bone reach very far forwards, it may be wise to cause this line to slant from before backwards (see dotted line _a_, Fig. 148). Unless this is done, it is found that in some feet so much of the wall is isolated at the bottom that insufficient is left to nail the shoe to. The next line to be made is the rear one. Its correct position is ascertained by first noting the junction off the wall with the bar (see groove 2, Fig. 149); and its inferior end must be just anterior to the inflexion of the wall. This is done that we may avoid cutting the bar. The position of the lower end of the rear line thus ascertained, it is run upwards with the chalk in the direction of the horn fibres.