I 
BONE-SPAVIN. 233 
experience and frequent dissections have fully demonstrated. Every 
practitioner, especially in cities, has frequently found a difficulty in 
satisfactorily locating the seat of lameness behind. Judging by the 
action of the hock, they have felt convinced that it was the seat of the 
disease, but the most careful examination of that joint, in the usual seat 
of spavin, fails to discover any enlargement, and very often they have 
come to the erroneous conclusion that the hip or stifle must be the seat 
of the cause of lameness, whereas, the articulations between the os cal- 
cis and astragalus in most of the occult hock lamenesses will be found 
in a diseased condition. 
In this form of spavin the lameness does not disappear by exercise 
to the same extent as in ordinary spavin; in fact, it is often increased 
by exercise, especially if on uneven ground. In these cases a very good 
test is to flex the hock, and by grasping the os calcis and moving it on 
. its articulations, it will cause pain and increase the lameness. 
A consideration of the position and uses of these two bones, and 
their connection to one another will readily indicate their liability to 
injury from over-exertion, slipping, and the usual causes of arthritis. 
The astragalus being subject to pressure from the tibia acting on its 
pulley-like surface in a direction from above downward and backward, 
and as remarked by Professor Williams, the peculiar screw-like motion 
of the joint is subject to three deviations : “ First, the direction is from 
within outward for a short distance, then it seems to run perpendicular¬ 
ly, and finally the lines of the prominence are seen to curve toward the 
inner side, and on to the inner third of the cuniform magnum.” 
This gives rise to action more or less twisting. The astragalus 
resting upon the cuneiform as its pedestal, is supported behind by the os 
calcis which clasps it as it were, resting upon it, and being supported 
by it. 
While the astragalus has to sustain sometimes enormous weight and 
compression, the os calcis is subjected to corresponding tractile force, 
applied by means of the powerful tendons which are attached to or 
play over its surface. Although we find it strongly bound in its posi¬ 
tion by powerful ligaments, we need not be surprised if we find that the 
articulations between these two bones, being exposed to such antago¬ 
nistic and often violent forces, frequently sustain such injury as to cause 
them to become inflamed, and be followed by all the concurrent pheno¬ 
mena of that accident. 
A knowledge of the above facts led me many years ago to adopt 
the plan of applying counter-irritation, not to the antero-internal part 
