[Illustration:  FIG. 140.—­EXCISION OF THE LATERAL CARTILAGE. (AFTER MOLLER AND FRICK.) a, The thinned horny wall covering the coronary cushion; b, the lateral cartilage exposed by stripping off the thinned wall; c, the sensitive laminae.]

This done, the external face of the cartilage is separated from the skin of the coronet.  To do this a double sage-knife is run flatwise between the coronary cushion and the cartilage, with the convex surface of the blade towards the skin.  The knife is then passed backwards and forwards until the necessary separation is accomplished.  During these movements of the knife a finger of the unoccupied hand should follow the knife, and guard the coronary cushion against injury.

Following this, the inner surface of the cartilage must be also separated from the structures lying beneath it.  To this end a sage-knife (right- or left-handed, according as to whether the anterior or posterior portion of the cartilage is to be first removed) is again passed into the incision.  With the cutting-edge of the knife forward, it is gradually reached round and under the hindermost end of the cartilage, and theposterior half of the cartilage separated from underlying structures, and at the same time excised by one clean cut forwards.  Using the second sage-knife in a similar manner, the cutting-edge this time backwards, it is reached in front of the cartilage, whose anterior half is then excised by a careful cut backwards.  Any small portions of cartilage remaining after this are sought for with the finger, and carefully removed by means of a scalpel and a tenaculum.

The fistulous opening or openings in the skin of the coronet should now be thoroughly curetted, and the whole of the wound dressed as to be described later.

In removing the anterior half of the cartilage it is highly important to remember the close contiguity to it of the synovial membrane of the pedal articulation.  This projects as a small sac between the antero- and postero-lateral ligaments of the joint.  Risks of injury to it may be diminished by having the foot secured with a line, and pulled forward by an assistant while the cut is being made.

Third Method (after Bayer).—­This operator recommends that, after stripping a half-moon-shaped piece of horn from the seat of operation, instead of raising the skin of the coronet and the attached coronary cushion in two flaps (as Fig. 139, a, a), that the cartilage be exposed by raising up one flap only (Fig. 141, a), consisting of a portion of the sensitive laminae, the coronary cushion, and the skin and underlying structures of the coronet.

With the horse cast and the preliminary steps over, the thinned horn of the quarter is incised in a semicircular fashion, and the half-moon-shaped piece thus separated from its surroundings stripped off.  At about 1/4 inch from the incision in the horn, a second incision of similar shape is made through the sensitive structures, which incision is also carried up into the skin and structures of the coronet.  This incision severs, from bottom to the top, (1) the sensitive laminae covering a portion of the pedal bone and a portion of the lateral cartilage, (2) the coronary cushion, and (3) the skin of the coronet and such structures as lie between it and the cartilage.