The operation is best performed by first grooving a line to connect the points a and c (Fig. 97).  This should run immediately under the coronary margin of the wall, and should stop short of injuring the coronary cushion beneath.  Grooves forming the sides ab and bc of the triangular piece of horn are next made, and the horn contained within the lines ab, bc, and ca, carefully removed.  The grooves are the easiest made by a cautious use of the firing-iron.  The greater thickness of the horn may thus be penetrated, and the grooves afterwards carried to their full and requisite depth by the use of the drawing-knife.

With the removal of the horn the diseased structures are exposed to view.  All such should be removed by a free use of the scalpel, and a suitable dressing afterwards applied.  A necessary factor in the treatment is the employment of pledgets of antiseptic tow.  With these the exposed tissues are covered, and the successive turns of a bandage run tightly over them, so as to exert a moderate degree of pressure.  When haemorrhage has accompanied the operation, this dressing should be removed on the following day, the wound dressed, and the pledgets of tow and the bandage renewed.  Any after-dressing need only then be practised at intervals of a week.  Repair after this operation is rapid, and takes place both from the exposed podophyllus membrane and from the coronary cushion.

[Illustration:  FIG. 97.  The dotted lines outline the V-shaped portion of wall to be removed in the treatment of complicated toe-crack.]

[Illustration:  Fig. 98.  The dotted lines indicate the portion of wall to be removed in the complete operation for complicated toe-crack.]

(d) By stripping the Wall from the Coronary Margin to its wearing Edge on Either Side of the Crack.—­This is merely a more extensive application of the method just described, and is only indicated in a complete and complicated crack that has refused to yield to other modes of treatment (see Fig. 98).

As in the previous case, a groove is run from a to c.  The grooves ab and de are then continued to the lowermost edge of the wall, and the whole of the wall within these points removed.  To facilitate removal, the white line should be grooved between the points b and d.  After-treatment is exactly the same as that just referred to.

B. CORNS.

Definition.—­In veterinary surgery the term ‘corn’ is used to indicate the changes following upon a bruise to that portion of the sensitive sole between the wall and the bar.  Usually they occur in the fore-feet, and are there found more often in the inner than in the outer heel.

The changes are those depending upon the amount of haemorrhage and the accompanying inflammatory phenomena occasioned by the injury.