d (navicular) bone, deep flexor tendon
(perforans) and adjoining structures. Whether it originates in the
flexor tendon or whether the bone is the original part affected, the
disease is frequently met, and of all possible causes, jars and
irritation incident to concussion of travel, are probably the principal
causative agents.

Symptomatology.--Lameness is the primary indicator and a constant
symptom which attends navicular disease wherever much structural change
affects the infirm parts. As the degree of intensity or extent varies,
so is there a dissimilarity in the character of the impediment.
Incipient cases of bilateral involvement are more difficult to diagnose
than are unilateral affections, particularly when lameness is not
marked. There is manifested a supporting-leg-lameness which varies as to
degree in the same subject at different times. This may be noticed
during the same trip in an animal that is being driven. There is a
tendency for the subject to stumble and, of course, where the affection
is bilateral, there is a stilted gait owing to shortened strides.

At rest the lame animal usually points with the affected member. Because
of the fact that the distance is lessened between the origin and
insertion of the deep flexor tendon (perforans) by this attitude, one
may readily understand the reason for the position assumed by the
subject. Pressure on the navicular bone is diminished and tension on the
flexor tendon is relieved by even slight volar flexion.

In acute inflammatory affections abnormal heat may be detected in the
region of the heel. By exerting tension on the flexor tendon, by means
of passive dorsal flexion of the member, evidence of hyperesthesia may
be detected. With the hoof testers one may determine supersensitivenss
in most instances. There occurs more or less contraction of the hoof in
navicular disease, but this is not to be taken as a cause of the
affection, but rather a sequence.

[Illustration: Fig. 32--"Pointing"--the position assumed by horse having
unilateral navicular disease.]

In some cases of unilateral navicular disease there is a marked contrast
in size between the sound and unsound foot. However, one must not be
misguided in this particular, for in some pairs of sound feet there
exists considerable difference in size. Finally, by a change from the
normal position of the foot to one in which the heel is somewhat
elevated (as may be obtained by shoeing with high heel calks),