62 
LAMENESS. 
from what is seen in caries or ulceration; and from this circum- 
stance has it acquired the denomination of porcellaineous de- 
posit. For our own part, however, we do not look upon it as any 
“ deposit” at all; rather, that there has been absorption: at the 
same time, no doubt, there has been a transmutation of the sub- 
stance remaining into firmer and harder material. 
Were we asked what occasioned this absorption, we should 
answer, pressure combined with friction ; and add, that the hock 
joint is the especial seat of these excavations, owing to the cir- 
cumstance of its being the joint most of all exerted in progression. 
We look upon their presence as fortuitous ; for they are not to be 
seen in all hock joints, and in some that are bone-spavined even 
are absent : nor can we, for our own part, see any use they serve, 
or any inconvenience they give, by their presence. 
Ossific Disease of Joints. 
The epiphyses of bones, entering into the formation of the 
joints, are frequently found encrusted with adventitious deposits 
of osseous matter, much augmenting their volume, and altogether, 
in many cases, altering their original shape ; and these crustace- 
ous bony deposits have their origin, commonly, in inflammation, 
chronic or acute, of the periosteal coverings of the epiphyses : we 
say “ commonly,” because it would appear that such changes of 
structure, and additions to it, do now and then take place without 
any precursory or accompanying inflammatory action, at least with- 
out any that is discoverable through outward signs. There is a 
very remarkable propensity in the horse’s economy to what is called 
ossific action : an injury of any kind — -a blow or kick, contusion or 
wound — -to the periosteum, exciting inflammation in it, is almost 
certain to be followed by exostosis. Inflammation — or even in- 
creased arterial action — excited in the same tissue from other 
causes, will give rise to similar conversion of it into bone. The 
same observation will apply to the elastic fibrous tissue uniting 
the small supplementary bones of the limbs to the shafts of the 
large straight bones to which they are articulated, the union being 
of a nature that warrants the appellation of joint; so that here is 
an example, and a very common one, of ossification of a joint. In 
fact, ossific disease commonly has its origin and nidus in one of 
these two fibrous tissues — the periosteal or the fibro-cartilaginous; 
and may, as was said before, be the result either of inflammation 
springing up in its own proper substance or spreading into it from 
some contiguous tissue. 
From the circumstance of our finding these adventitious osseous 
deposits for the most part in the vicinity of joints, as well as from 
