ane is a synovia-secreting one, and
bearing in mind what happens in ordinary synovitis and arthritis (with
which, of course, this may be very closely compared), we shall first expect
changes in the bursal contents. It is highly probable, though difficult of
proof, that in the very early stages the chronic inflammatory stimulus has
the effect of increasing the flow of synovia. In every case, however, where
it can with any certainty be said that navicular disease exists, it is too
late to meet with this condition. The disease has then progressed until
destruction of the secreting layer of the bursal membrane has been
seriously interfered with, and in this case we find a distinct deficiency
in the quantity of synovia in the bursa. In advanced cases it is even found
that the bursa is _absolutely dry_.

2. _Changes in the Cartilage_.--Directly that portion of the bursal
membrane covering the cartilage is the subject of inflammatory change, the
cartilage itself, by reason of its low vitality, soon suffers.

Under a process, which we may term 'dry ulcerative,' the cartilage covering
the ridge on the lower surface of the bone commences to become eroded, and
in appearance has been likened, both by English and Continental writers, to
a piece of wood that has been worm-eaten (see Fig. 161).

[Illustration: FIG. 161.--NAVICULAR BONE (POSTERO-INFERIOR SURFACE) SHOWING
THE 'WORM-EATEN' APPEARANCE CAUSED BY EROSION OF THE HYALINE CARTILAGE, AND
COMMENCING RAREFACTIVE ARTHRITIS.]

'At this stage, or much earlier'--we are quoting Colonel Smith,
A.V.D.--'may be found calcareous deposits in the fibro-cartilage and the
bone. They are scattered like fine sand here and there, generally across
the inferior half of the face of the bone; they are sometimes numerous,
frequently scanty, occasionally entirely absent. The amount of calcareous
degeneration depends upon the lesions present. If much destruction of bone
exists, there will be but few calcareous deposits; whilst if there are many
calcareous deposits, there may be but slight ulceration of bone tissue, and
perhaps none at all. In fact, I have held the opinion, and see no reason to
modify it, that calcareous deposits are safeguards against caries.'[A]

[Footnote A: _Journal of Comparative Pathology and Therapeutics_, vol. vi.,
p. 195.]

3. _Changes in the Tendon_.--The effect of these calcareous deposits on
the under surface of the bone is to produce a certain amount of roughness.
Seei