514 
A. ZUNDEL. 
bone. It must be observed that in this complex action of decom¬ 
position of the shock, the os sesamoid, though pushed from before 
backward by the os coronse, is, however, supported by the resist¬ 
ance of the perforans tendon. Consequently, both the bone and 
the tendon are pressing upon each other, when the feet are placed 
on the ground, throwing the body forward by the impulse of the 
hinder parts, and thus press powerfully against each other. 
When this pressure takes place in an animal going full speed, 
and a good and high stepper, it may commence by becoming 
merely a slight contusion, but, if often repeated, the result may 
be some lesion upon the corresponding surface of the bone and of 
the tendon, or of the synovial which facilitates their movements. 
But the energy of action in the animal cannot be considered the 
only producing cause of these lesions, as a vice of conformation 
in the foot, a want of elasticity in its posterior parts where the 
resisting power is diminished, may also produce it. The disease, 
then, is observed in animals whose plantar cushion, covered by a 
small, dry and atrophied frog, is itself badly developed, from 
being compressed between the bars, which are more vertical, or 
the heels, which are more contracted; all these being conditions 
which diminish the flexibility of the back of the foot. 
Two principal causes, then, co-operate in the genesis of 
navicular disease, and are almost always present in animals thus 
affected. On the one hand, it will appear amongst well-bred ani¬ 
mals, especially those of English breeds, those from Hanover, 
Mecklenburg and Normandy, which will be more affected. 
Loiset and Lafosse, however, have seen it in common breeds, in 
animals with flat feet and soft horns. Lafosse says he has seen it 
in mules. But besides this influence of the breed, there is the 
effect of what we may denominate the hygiene of the foot: the 
too dry bedding, certain wrong modes of shoeing and all the pre¬ 
disposing causes of contracted heels. Let us add also, as a cause, 
the effect of changing the animals from marshy fields, where they 
were walking on soft, damp ground, to stables with dry bedding— 
a cause commonly present in horses transported from Northern 
Germany to the south. Hard work and excessive exercise are 
also causes of this affection—for example, jumping fences with a 
