vicular disease.
The operation of neurectomy was ultimately had recourse to. The horse
subsequently did his work as well as ever, and was ridden to hounds
regularly till the end of the year 1861, when he went lame of the off
fore-foot. From this date he also showed very peculiar action behind, and
was at times lame of both hind-limbs without any apparent cause.

'In the year 1862, from the groom's indiscreet use of physic,
superpurgation was brought on which caused the animal's death. On a
post-mortem examination being made, the horse was found to have _navicular
disease of all four feet_. It is worthy of note that this horse had
always "extravagant" action behind, but was a remarkably quick and good
jumper.'[A]

[Footnote A: F. Blakeway, M.R.C.V.S., _Veterinarian_, vol. ii., p. 21.]

_Differential Diagnosis_.--Navicular disease may be mistaken for ordinary
contracted foot. It will be remembered, however, that in the early stages
of navicular disease contraction is absent, and that it is only when the
disease in the bursa is of long standing that contraction comes on. With
ordinary contracted foot, too, careful paring and suitable shoeing soon
sees a diminution in the degree of lameness, and a return to the normal in
shape (see Treatment of Contracted Foot, p. 125). With navicular disease,
however, such shoeing as is beneficial in the treatment of contracted foot
(notably the various methods of giving to the frog counter-pressure with
ground) soon brings on an aggravation of the lameness.

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 condition 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 extension 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 gui