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 lay