TREADS AND INJURIES TO THE CORONET. 
785 
position. Daring acute inflammation the papillae of the coronary band 
aie displaced relatively to one another, and must regain their former 
position before they can again produce a normal growth of horn. This 
is effected b}^ the neighbouring papillae, which have not suffered dis¬ 
placement. As the growth of horn starts from the periphery of the 
injury, the diseased and displaced papillae are gradually brought into 
position by the growth of neighbouring horn tubules; and as repair 
proceeds, the normal state is restored. Sometimes the growth of horn 
is irregular, because it sets in before swelling has completely disappeared, 
and the papillae are unable to take up their normal position; or, again, 
horn production does not proceed regularly from the periphery towards 
the centre of the injury. The displaced papillae then become fixed in 
their abnormal position, and produce a horny prominence on the 
coronet, in consequence of certain of them not contributing to the 
formation of the wall, but producing disconnected masses of horn. The 
horny wall then shows a defect at the point in question, which detracts 
from its solidity. Sometimes the exterior of the wall is thickened, 
because horn formation goes on while the coronet is still swollen. In 
exceptional cases, this thickening may take place on the inner surface, 
producing a keratoma. 
In addition to such complications, more dangerous consequences may 
follow treads. If, for instance, in consequence of direct injury to the 
joint, its perforation by pus during an attack of purulent cellulitis in 
the subcoronary connective tissue, or of extension of necrosis towards 
the depths, purulent or septic inflammation attacks the pedal-joint, the 
condition becomes incurable. 
Necrosis of the extensor pedis tendon produces severe lameness; when 
the foot is extended, or attempts are made to bear weight on it, the 
lower part of the limb assumes a position of excessive volar flexion. 
The condition, however, may involve no permanent injury, the defect in 
the tendon being replaced by connective tissue, which firmly unites the 
ends. Extension of necrosis to the sensitive laminae is dangerous, because 
of its tendency to involve large areas, leading to diffuse inflammation of 
the sensitive structures, which may be followed by loss of the hoof. 
Necrosis of the lateral cartilage always produces quittor. 
Prognosis. The consequences of treads may be exceedingly varied. 
The following points are of chief importance :— 
(1) The position and extent of injury. The more nearly the injury 
approaches the band, the graver it becomes. If the skin and upper part 
of the horny wall are alone injured, and the wound is not deep, healing- 
soon follows ; but treads on the coronary band not only offer great 
obstacles to treatment, but may involve the pedal-joint, especially in 
the small, clean feet of well-bred horses. At the centre of the toe the 
3 E 
v.s. 
