NAVICULAR DISEASE. 545 
pedis. The posterior fate of the navicular bone should be beautifully 
smooth, and lined by synovial membrane which forms a lubricating sac 
for it to play upon, and thus take off the friction between the tendon and 
the bone. Such is nature’s provision against mischief in this delicate 
part of the machinery of the foot, which she keeps in order by the con- 
stant supply of synovia or joint oil. But when the sac is not stimulated 
to a healthy action by the pressure of the frog below it in doors and out, 
synovia is no longer secreted in proper quantity, and as soon as the horse 
is put to hard work inflammation takes place for want of it. The result 
is some one of the consequences of inflamed joints. Either ulceration 
takes place in the postero-inferior surface, where the tendon glides over it 
as shown in fig. 2 (at 3), sometimes ending in caries of the bone itself ; cr 
adhesion takes place without ulceration of the tendon with the surface of 
the bone, or there are small exostoses thrown out, see fig. 2 (2), or lastly 
there is simple inflammation without either adhesion or ulceration, and in 
this stage the disease is amenable to treatment without leaving any trace 
behind. 
The symptoms of navicular disease are the same, whether the mischief 
has extended to ulceration or not; but the history will guide us in ascer- 
taining how far it has gone. Of course they vary in degree, for there 
may be only a slight extent of ulceration, or a high degree of simple 
inflammation; but in the former case the lameness will not be so marked 
as in the latter, though the prospect of recovery will be much less.’ There 
is always more or less lameness ; but, in consequence of its affecting both 
feet, it is not so marked to the careless observer as in some much more 
trivial cases where only one is diseased. The distinguishing sign, though 
not absolutely infallible, is the pointing of the toe, and a peculiar round- 
ing forward of the fetlock joint, so as to relieve the navicular bone 
of any weight. In laminitis, the object of the sufferer is to relieve all 
pressure as much as possible, by bringing the hind legs under the body, 
and by bearing the weight of the fore quarter on the heels. Here, the 
reverse of the latter attitude is observed—the heels are not allowed to take 
any pressure, and the toes alone are placed at all firmly on the ground. 
This is marked in the stable by the pointing of the toe (in each fool 
alternately, if both are diseased, but in the one only, if they are not both 
alfected). Out of doors, the toes dig into the ground, the heel never 
being brought firmly down, and frequent stumbles mark the difference 
between this species of lameness and laminitis. The subject of navicular 
disease generally walks sound ; but the moment he is trotted, he goes as 
if his legs were tied together, his stride being shortened in a remarkable 
manner, but without exhibiting the peculiar fumbling gait of the foun- 
dered animal. As in his case, soft ground suits him, and he has no fear of 
plough, because his sole is hard and unyielding. Many tolerably cot- 
firmed cases of navicular disease may, therefore, be hunted, except when 
the ground is hard, supposing, of course, that they are kept off the road ; 
but no plan of management will enable them to bear the jars incidental to 
harness-work or hacking. When one foot only is the subject of navicular 
disease, it often happens that it is smaller altogether than the other ; but 
it is somewhat difficult to say whether this is a cause or a consequence of 
inflammation. One thing is quite clear, that many horses are met with, 
still perfectly free from lameness, in which there is a difference of size in 
their fore feet; but whether or no these are afterwards invariably the 
subjects of navicular disease, it is almost impossible to ascertain. It is, 
however, the general opinion, founded on experience, that when this 
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