The seat of corns is either on the fleshy leaves of the quarters, or on the velvety tissue of the sole in the angle between the wall and the bar, or on the fleshy leaves of the bars. Thus we distinguish corns of the wall, sole, and bars.

Corns affect chiefly the front hoofs, and more often the inner half than the outer. Unshod feet are seldom affected.

According to the intensity of the lesions we distinguish:

1. Dry Corns.—The red-stained horn is dry, and there is seldom lameness.

2. Suppurating Corns.—They are the result of intense bruising followed by inflammation. The pus is either thin and dark grayish in color, denoting a superficial inflammation of the pododerm, or yellowish and thick, denoting a deep inflammation of the pododerm. In the latter case a veterinarian should be called. Lameness is usually pronounced.

3. Chronic Corns.—In this case there is vivid discoloration of horn in all possible hues. The horn is either soft, moist, and lardy, or crumbling, cracked, and at times bloody. The inner surface of the horn capsule has lost its normal character, and is covered with horny swellings or nodules ([Fig. 192, a]). Sometimes the wing of the os pedis on that side has become morbidly enlarged and loosened. A short, cautious gait alternates with well-marked lameness; the latter appears whenever the shoe presses too firmly on the corn, or when the hoof becomes too dry.

Fig. 192.

Inner aspect of a quarter of a hoof, showing changes in the horn-leaves due to chronic corns: a, horny tumor resulting from the disease.

The causes, aside from the form and quality of the hoofs and the position of the limbs, lie in injudicious dressing of the hoof and in faulty shoes. Too much trimming of wide and flat hoofs, excessive weakening of the quarters, sole, bars, and frog of all other hoofs, while the toe is usually left too long, are the usual causes. Shortening one quarter too much in relation to the other, so that the foot is unbalanced and the lower side overloaded, is a frequent cause. Hollowing the sole and bars excessively and unnecessary thinning of the branches of the sole in the search for corns are also causes.