3. That this tendency to contraction will at first appear in the thinner portion of the area of wall named—namely, in that immediately below the bulging coronary margin.
We thus get the appearance depicted in Fig. 79—a contraction (a, a) of the heels in the horn below the coronary margin, with the coronary margin itself bulging above, and a hoof of apparently normal width below.
We say 'apparently' with a purpose, for, as actual measurements will show, the wall near the solar edge is really contracting, for reasons which we have just described connected with shoeing. Its 'appearance' of normal width is accounted for thus: The contraction at a, a is caused by the dragging inwards of the coronary cushion brought about by the sinking downwards of the plantar cushion, with which body it will be remembered the coronary cushion is continuous. With the constant dragging in and down of the coronary cushion there is given, to the horn-secreting papillæ, studding both the lower third of its outer face and its lowermost surface, a distinct 'cant' outwards. Below the lowermost limit of the coronary cushion, then, by reason of the cant outwards of the coronary papillæ in the situations mentioned, the horn of the wall takes a more outward direction than normal, a fact which lessens in effect the contraction as a whole really going on. It is interesting, too, to note that by this outward cant of the wall below, and the bulging of the coronary margin above it, the contraction (a, a) is heightened in effect, and caused to appear greater than really it is.
From what we have said it follows that contraction of the heels, excepting the extreme coronary margin, is existent generally, and not confined solely to a, a.
We have, then, in this condition, as we indicated at the commencement, but a phase in the evolution of ordinary contracted heels, for, with the progress of the contraction already existing at a, a, and below those points, it is only fair to assume that with it falling in of the at present bulging coronary margin must sooner or later occur, that, though expanded when compared with the wall below it, it will be really contracted as compared with what it was once in that same foot.
We may therefore conclude this section by remarking that factors tending to contraction of the heels in general are equally potent in the causation of contracted coronet alone.
Treatment.—Exactly that described for contracted heels. Bearing in mind that contracted coronary margin is but the onset of contracted heels, and that its first exciting cause is that of removal of the ground-pressure upon the frog, the most careful attention must be paid to the shoeing. The use of bar shoes, ordinary frog pads, or heelless shoes and bar pads, are especially indicated, together with abundant exercise. By these means the normal movements of expansion will be brought into play, and the condition quickly remedied.
C. FLAT-FOOT.
Definition.—By this term is indicated a condition of the foot where the natural concavity of the sole is absent.
Symptoms.—In the flat-foot the inferior edge of the wall, the sole, and the frog, all lie more or less in the same plane. It is a condition observed far more frequently in fore than in hind limbs, and is seen in connection with low heels, more or less obliquity of the wall, and a tendency to contraction. The action of the animal with flat feet is heavy, a result partly of the build of the foot, and partly of the tenderness that soon comes on through the liability of the sole to constant bruising.