Although commencing in the insidious manner we have described, the lesion is not thus often seen by the veterinary surgeon. Usually, the animal with sand-crack is brought for his inspection when lameness has arisen from it. In this case the cause for the lameness will reveal itself in the crack, which is now too large to escape observation. The coronet is hot and tender to the touch, and a sensation of warmth is sometimes conveyed to the hand by the horn of the surrounding parts of the wall. It is hardly necessary to say that, with accompanying conditions such as these, the sand-crack is a _deep_ one. Where the lameness is but slight, we may attribute it almost solely to the pain occasioned by the mere wounding of the keratogenous membrane, and to no very extensive inflammatory changes therein. By some authorities this is said to be due to the pinching of the sensitive structures between the edges of the fissure in the horny covering. In our opinion, however, pinching does not occur unless inflammatory exudation into the sensitive structures adjoining the crack has led to sufficient swelling to cause them to protrude. In other words, the movements of the horny box, communicating themselves to the structures beneath, and so occasioning movement in the wounded keratogenous membrane, are quite sufficient to give rise to the lameness without actual pinching of the structures implicated. The severity of the lameness will vary with the rapidity of the gait, and with the character of the road upon which the animal is made to travel. For instance, many animals in which the lameness is imperceptible at a walk become 'dead' lame at a fast trot. It is sufficiently explained when one remembers the greater movements of expansion and contraction of the posterior parts of the wall brought about by the increase in the rate of progression. The same animal, too, will go distinctly more lame upon a hard than upon a soft surface. In like manner the lameness from toe-crack also varies in degree with the rate of progression and the character of the travelling, though not to such a noticeable extent as in the lameness from quarter-crack. A greater variation may in this case be brought about by moving the animal on ascending and descending ground. Descending an incline, with a more than ordinary share of the body-weight thus thrown upon the heels, the lameness is most marked. The reason would appear to be that the greater expansion of the wall of the heels thus brought about leads to a proportionate contraction of the wall at the toe, especially at the edges of the crack, thus causing undue pressure upon the exact spot of the wound in the sensitive structures. Ascending--the weight in this case transferred from the posterior to the anterior portion of the foot--the expansion of the heels becomes a contraction, with a corresponding lessening of the contraction at the toe and a distinct decrease in the lameness.