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.
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.
