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440, DISEASES OF THE HORSE’S FOOT 
It is, perhaps, even more likely to be confounded with 
contraction when we have with the contraction a state of 
atrophy and thrush of the frog. With a frog in this condi- 
tion pressure will give rise to pain, and navicular disease be 
erroneously judged to be present. In such a case we must 
rely wholly upon either extreme flexion or extreme exten- 
sion of the joint to guide us, when, if contraction only is the 
offending condition, no symptom of pain will be shown. 
Navicular disease may also be confused with rheumatic 
affections, with sprain of the posterior ligaments of the first 
interphalangeal articulation, and with sesamoid lameness. 
Mistakes are sometimes made, too, especially with a hasty 
observer, in confounding it with shoulder lameness. 
In rheumatism the constant changing of the seat of pain, 
the sometimes elevated temperature, and the appearance of 
symptoms of heat, tenderness, and swelling in the affected 
area should guide one to a right conclusion. 
In sprain of the posterior ligaments of the coronet and in 
sesamoid lameness, nothing but a careful examination and 
manipulation of the parts will ward off error, for in each of 
these cases there is ‘ pointing’ and resting of the limb, and 
considerable disinclination to put weight firmly upon it. 
If at the same time manipulation gives distinct evidence of 
pain, all doubt may be set at resi. 
Roughly speaking, sesamoid lameness is a condition of 
the gliding surface of the sesamoids, and the face of the 
tendon playing over them, similar to that found in navicular 
disease. All symptoms of pointing, the constant main- 
taining of the limb in a state of flexion, and a feeling 
manner of progression are again all present. It is plain 
from this that in all cases where an animal with a gait at all 
suggestive of navicular disease is brought for our examina- 
tion, the manipulation of the limb should be thorough. 
The character of the lameness is almost sure to deceive us; 
and it is not until we are able to obtain local symptoms 
pointing to the one or the other of the conditions we have 
enumerated that a decisive opinion may be given. In 
sesamoid Jameness the local symptoms are those of heat 
