78 WEST OF ENGLAND VETERINARY MEDICAL ASSOCIATION. 
from being kept too long in a stall or small place, — the feet undergo 
changes, all the tissues become altered in character for want of 
exercise, the circulation is impeded, congestion takes place, and an 
altered character of the horny secretions resulting, the hoof loses 
its normal elasticity, and when brought into action, does not yield 
so readily to pressure ; consequently, the navicular bone is more 
likely to be affected by concussion and compression. In all cases 
where one foot is smaller than the other, it must be looked upon 
with suspicion, even if no lameness is apparent. There are no 
positive demonstrable signs of the early stages of navicular disease. 
In the absence of all appearance of disease in any other part of the 
foot, or leg, the experienced practitioner is soon able to state that it 
is a case of navicular disease ; if it has existed long, there will be 
generally (not invariably) alteration of structure of the inner quarter 
or heel of the wall. Feet which are small at the top, and spread 
out wide at the bottom, commonly called bell-shaped, are very much 
predisposed to disease. 
Causes . — Hereditary predisposition, bad shoeing, the feet being 
cut and reduced too much, the shoes made either thick at the heels, 
or with caulkings, standing in a stall too long without work or exer- 
cise. The disease is often produced in young horses, from their 
being made to go too fast (not necessarily long journeys) before 
they have been properly conditioned by previous walking exercise. 
Injuries to other parts of the limb, causing the animal to be confined 
to a small place for a long time, may, from the inaction, produce 
not only navicular disease, but also laminitis, seedy foot, contraction, 
or an atrophied state of the hoof, the result of perverted nutrition 
consequent upon a congested state of the vessels of the feet. But 
the cause of causes is the pace, heavy weight, and excessive exertion 
over hard roads, producing concussion and compression of the 
navicular bone. 
Pathology . — I have stated before, that it has been long taught 
by some that the disease commences in the synovial membrane 
covering the cartilage ; however, that cannot be, as there are no 
synovial membranes covering articular cartilages. 
Neither can it be, as the late Professor Dick taught, sprain of the 
tendon, for when a tendon is subjected to repeated strains sufficient 
to produce lameness, thickening instead of attenuation is the 
result. Another important point to be recognised in the con- 
sideration of diseases of this joint is, that there is no primary 
disease of the articular cartilages, for pathological anatomy teaches 
us that all the changes that are found in it are secondary to some 
other affection of the bone ; there is no such thing, therefore, as 
primary ulceration of the cartilages ; when cartilage is diseased, it 
is from the extension of mischief from the bone beneath. Arti- 
cular cartilages are not vascular, they are nourished by cell im- 
bibition. 
The first stage of navicular disease is that of congestion of the 
bone, and it may be so slight as to quickly pass away with a little 
exercise ; but if the same cause is still in operation, the congestion 
