630 OSSIFICATION OF THE LATERAL CARTILAGE. SIDE-BONE. 
hind; 3, the cartilage of the left hoof suffers more frequently than 
that of the right ; and 4, the outer cartilage suffers more frequently than 
the inner. 5. Ossification sometimes occurs at an early age, usually 
when the animal is first put to work. 6. Well-bred animals suffer less 
frequently than others. 7. The use of animals, of heavy build, on hard 
roads favours the occurrence of side-bone. 
The symptoms vary according to whether one or both cartilages are 
affected, and whether ossification is partial or complete. Expansion of 
the hoof is always diminished, and may be entirely suspended. Side- 
bones produce a clumsy, constrained action, and at times marked lame¬ 
ness. The symptoms are aggravated by rapid work on hard roads, by 
allowing the hoofs to become dry, and by using high calkins. When, 
Fig. 247.—Pedal bone, with almost complete ossification of the lateral cartilages, a, Pedal 
bone ; b, wing of pedal bone, from which point, as a rule, ossification commences ; c, 
articular surface ; d, rough, uneven surfaces of the ossified cartilages. 
however, the hoof is kept moist, animals may work for a long time 
without inconvenience. 
The diagnosis of side-bone is easy as soon as the upper margin of the 
cartilage has become ossified; it then feels hard. On the other hand, 
when ossification has only attacked the lower portion of the cartilage 
lying within the hoof, it is either very difficult or absolutely impossible 
to detect the change, though the form of the hoof sometimes gives 
valuable indications. 
The causes are— (1) congenital predisposition, in heavy, coarse-bred 
horses; (2) excessive concussion produced by work on hard roads, for 
which reason the disease is frequent in large towns; and (3) shoeing 
with calkins, by which the frog is prevented taking any bearing on the 
ground and the lateral cartilages are subjected to a continuous inward and 
downward dragging strain. This is concentrated at the fixed, he., anterior, 
end of the cartilage, where disease usually commences. Mechanical 
injury is another undoubted cause. This, and the fact that the outer 
