The pus formed in this condition may remain confined to the coronet and break through the skin as an ordinary abscess, or it may, before so doing, burrow beneath the wall, and invade the sensitive laminae.  In this case, whenever portions of the secreting layer of the keratogenous membrane are destroyed, or perhaps only temporarily prevented from fulfilling their horn-producing functions, then corresponding cavities in the horn are the result (see Fig. 109).

(b) Purulent Arthritis.—­Only too readily the pus so formed tends to penetration of the articulation and the causation of an incurable arthritis (see Chapter XII.).

[Illustration:  FIG. 109.—­MESIAL SECTION OF A HOOF ILLUSTRATING THE CONDITIONS FOLLOWING UPON CORONITIS. a, Cavity in the horn of the wall; b, enlargement of the coronet and the horn of the wall following subcoronary suppuration; c, cavity in the wall following purulent inflammation of the sensitive laminae; d, hollow in the horn of the sole consequent upon suppuration of the sensitive sole.]

(c) Necrosis of the Extensor Pedis.—­This may arise either as a result of spreading purulent infection of the coronary cushion, or as a result of direct injury immediately over it.  The close relation of the terminal portion of this tendon with the pedal articulation, and the incomplete protection from outside injuries here afforded to the joint by the horny box, sufficiently points out the gravity of the condition.

(d) Penetration of the Articulation.—­This also may be a result either of the inroads made by pus, or of an actual wound.  When occurring from the latter, it is seen more often than not in the hind-foot, being there caused by the calkin of the opposite foot.  Where a wound in this position is characterized by an excessive flow of synovia, the condition should be suspected, and, if the wound be large enough, the little finger should be introduced in order to ascertain.  Needless to say, the injury is a grave one.

(e) Sand-crack.—­Sand-crack is likely to result from tread when an injury is inflicted in the region of the quarter by a severe overreach.  Treads, too, especially with the calkin of the hind-shoe, are especially apt to end in this way.  In this latter instance the sand-crack usually has its origin in a nasty jagged tear at the top of the wall of the toe.

(f) Quittor.—­In one respect any suppurating wound at the coronet may be deemed a quittor.  By indicating quittor as a complication of coronitis, however, we denote the more serious form of this disease, in which the wound has taken on a sinuous character, and conducted pus to invasion of the lateral cartilage.  It is one of the worst complications we are likely to meet with in this condition, and will be found fully described in Chapter X.

(g) False Quarter.—­This complication of coronitis occurs when the injury or after-effect of the formation of pus has been severe enough to destroy outright a comparatively large portion of the papillary layer of the coronary cushion.  To this condition we devote Section D of this chapter.