W. L. ZUILL. 
.252 
ism also predisposes to bone spavins. An animal driven at any 
speed whatever places his foot upon an inequality of the pave¬ 
ment, which gives it an inward or outward inclination, thus tend¬ 
ing to throw the body in an opposite direction. Between these 
two forces there is a tendency to flexion of the hock joint from 
side to side (an impossible normal movement), which is resisted 
entirely by the lateral ligaments of the joint, frequently result¬ 
ing in laceration of the fibres and rupture of their periosteal 
attachments. 
In this case the power is the weight of the body, the point 
of resistance is the hock.. Under such conditions the resistance 
offered to this force is lessened in proportion as the short arm of 
the lever is reduced by narrowing the hock. On the other hand, 
the resistive power increases rapidly and in direct ratio to the 
increased width of the articular surfaces. The ligamentous 
structures of the joint are less apt to be injured than the bone to 
which it is attached; hence it follows that these injuries will re¬ 
sult in an inflammation of the bone, the deposit of lime salt, and 
the formation of an exostosis, which if on the inner side of the 
joint, is called bone spavin. 
These two forms of spavin, the inter-articular and the bone 
spavin, often exist in the same joint, and may mechanically inter¬ 
fere with the function of the articulation of the astragalus, with 
the cuboid and scaphoid; or these with the two cuneiforms, or 
they in turn with the metatarsal bones. Muscular effort of any 
kind superinduces lesions of the tendon of the flexor metatarsi 
or its attachment on the small cuneiform and head of the in¬ 
ternal rudimentary metatarsal. Its synovial sheath is compro¬ 
mised by the same class of causes. 
One very important point to be considered is the hereditary 
predisposition in this group of diseases. When a mare, or horse, 
with spavin is used for breeding purposes, the progeny will in¬ 
herit the weakness of its parents; that is to say, hock joints de¬ 
ficient in their development and therefore prone to these diseases. 
Such animals should never be used for stock purposes. It is my 
-opinion that animals with defective or deficient hocks should not 
