SPAVIN. 
465 
Another though less common seat of the disease is the surfaces 
of articulation between the astragulus and os calcis, and in this 
location the disease usually partakes of the nature of a true 
form of osteoarthritis, and often terminates in caries and necro- 
sive ulceration within the joint. 
Pathology .—The inflammation occurring in spavin may be 
considered of two distinct forms, namely : acute and chronic. 
The disease may arise from two causes, namely : Idiopathic 
and traumatic. Under the first head may be included all 
hereditary predispositions to osseous exostosis, due primarily to 
defective anatomical construction of the skeletal framework, 
the usual result of which is endositis, periostitis and osseous 
exostosis of the bones of the articulation. Under the second 
head we include all external agencies that directly or indirectly 
cause the disease, such as concussion, severe strain or stretching 
of the ligaments of the joint, more especially the interosseous 
ones ; injuries, such as kicks, wounds, etc. ; though in my ex¬ 
perience spavin is rarely due to injuries of a direct nature, 
though an injury may be the indirect cause of spavin, as where 
the opposite limb has been injured and the animal in favoring 
it throws the entire weight of the posterior part of the body 
upon the sound limb, which in time may become affected with 
spavin. 
The question is often asked, Why does spavin most gener¬ 
ally appear at the junction of the cuneiform magnum and par- 
vum ? In viewing a tarsus in profile, we notice that the bones 
of the joint do not rest upon a plane surface, but incline grad¬ 
ually from the external part of the joint to its internal portion ; 
we also note a greater development of the bones composing the 
external part of the tarsus than those of the internal portion. 
This removes slightly the line of gravity from the central part 
of the joint towards its inner part, and as a result the line of 
weight descending from the tibia to the surface of the astragu¬ 
lus is thrown in an oblique manner mostly upon the inner por¬ 
tion of that bone, and is in turn transmitted to the inner part 
of the scaphoid, cuneiform magnum, and parvum. The parvum 
