'The horse-nails are prepared in the ordinary way as for driving, with the exception that each is pointed on the reverse side, to prevent puncturing the sensitive structures. Before being used the nails are put in a vice, and the head hammered to form a shoulder, to prevent their being driven too far into the wall, and breaking out the hold.'[A] [Footnote A: _Veterinarian_, vol. xlviii., p. 100.] Before driving the nail some operators burn or bore a hole for it. Opinion seems to differ as to whether this is at all necessary. A method of clamping which, on account of its simplicity, has become greatly popular, is that of Vachette. For this operation is needed the outfit depicted in Figs. 86 and 87. [Illustration: FIG. 87.--THE SAND-CRACK FORCEPS AND CLAMP.] With the special firing-iron (Fig. 86) an indentation, sufficiently large to admit the points of the clamp (Fig. 87), is made on each side of the crack. The clamp is then adjusted, and pressed home tight by means of the sand-crack forceps (Fig. 87). According to the length of the crack, one, two, or three clamps may be necessary. Another useful clamp, though far more complicated in its structure, is that of Professor McGill (Fig. 88). [Illustration: FIG. 88.--MCGILL's SAND-CRACK CLAMP.] 'The object of this invention is to arrange on a spindle, which is screw-threaded at one end with a right-hand thread and at the other with a left-hand thread, two clips or clamps, free to travel on the thread, there being a nut between the two which can be turned by a spanner. The clips are placed on the hoof, one on each side of the sand-crack, the hoof being prepared to receive the instrument by filing a groove or notch for the clamps to fit into, and by turning the nut on the screw the clamps are brought towards each other, and the crack thus prevented from spreading.'[A] [Footnote A: _Veterinarian_, vol. lxi., p. 141.] Still a further useful clamp is that of Koster. This is considerably broader than the clamp of Vachette, and its gripping edges are provided with teeth (see Fig. 89). As with the clamp of Vachette so with this, a groove is burned into the wall on each side of the crack for the accommodation of the jaws of the instrument, and the clamp itself pressed home by means of a special pair of forceps. This form of clamp holds well, and has the advantage of securing a wider area of horn than that of Vachette or McGill. [Illustration: FIG. 89.--KOSTER'S SAND-CRACK CLAMP.] Clamping by any method should be advised or undertaken only under certain conditions. The horn should be moderately strong, and the wall should be thick. This practically restricts the use of the clamp to cracks of the toe, and it is there, as a fact, they are found of most benefit. While burning the grooves for the clamp, and while tightening the clamp itself, the animal's foot should be on the ground and bearing weight at the heels, thus insuring the greatest possible approximation of the edges of the crack.