SPAVIN. 
467 
Haversian canals and cancelli, that the inflammation occurs, 
and that the pathological process, though somewhat modified 
by the hard and resisting nature of the osseous frame¬ 
work, is essentially similar to that which occurs in the soft 
tissues.” 
In the endositic form of spavin, as the inflammation ad¬ 
vances the peripheral lamellae and the articular cartilage become 
involved in the destructive metamorphosis, in which the canal- 
iculi of the opposing bones are laid bare by the constant fric¬ 
tion and irritation, thus establishing a vascular communication 
between the Haversian canals and lacunae of the bones. These 
vascular openings pour out an effusion of bone-forming lymph, 
which in time firmly cements the diseased bones together. We 
see this condition finely illustrated in the specimen before you, 
in which it will be seen that the scaphoid, cuneiform magnum 
and parvum are firmly cemented together without there being 
the slightest periostitic enlargement on the external borders of 
the bones. 
In the periostitic form of spavin the inflammation advances 
from the periphery of the bones to their centre, and, as before 
mentioned, is usually due to external influences, such as strain 
of the interosseous ligaments, articular arthritis, violent over¬ 
contraction of muscles or tendons implanted in the periosteum 
of the bones. “The pathological changes in circumscribed 
periostitis consists of an inflammatory transudation into both 
the superficial and the deeper strata of the membrane, forming 
an enlargement sometimes termed a ‘ node.’ This transudation 
consists of fibrous lymph and leucocytes, which serve to form a 
prominence over the surface of the bone.”—Agnew. This in¬ 
flammatory node in the horse, when affecting the bones of the 
tarsus, constitutes the osseous exostosis termed spavin. 
Etiology .—Spavin is a disease due to domestication. It is 
rarely seen among equidse living in a state of nature. The 
horses that live on the plains and in the valleys of the Rocky 
Mountain regions of the United States, Canada and Mexico are 
rarely affected with spavin. 1 am reliably informed that among 
