_Pathology and Point of Commencement of the Disease_.--The exact position in which the diseased process starts has for a long time been a subject of discussion, and even now it is doubtful whether the point has been definitely settled. To mention but a few among many: We find Mr. Broad, of Bath, strenuously insisting on the fact that the disease commences in the interior of the navicular bone. Just as strenuously we find the editor of the journal in which the matter is being discussed, the late Mr. Fleming, asserting that the disease commences in the bursa.[A] Others, too, hold that the disease commences primarily in the tendon. Wedded to this view was the discoverer, Mr. Turner, of Croydon; while Percival commits himself to the statement that it is either the central ridge or the postero-inferior surface of the navicular bone, or the opposed concavity in the perforans tendon, that shows the earliest signs of the disease. The observations made by Dr. Brauell, the first Continental writer to fully describe the disease, led him to the statement that neither the bone nor the bursa was the _invariable_ starting-point of the trouble, but that usually it commenced in inflammation of the bursa itself. [Footnote A: Percival's 'Hippopathology,' vol. iv., p. 132.] Without, therefore, committing ourselves to an expression of opinion as to the precise starting-point of the affection, we shall describe the pathological changes occurring in navicular disease as noted in (1) the bursa, (2) the cartilage, (3) the tendon, and (4) the bone. 1. _Changes in the Bursa_.--Upon the internal surface of the bursal membrane is first noticed a slight inflammatory hyperæmia, accompanied by more or less swelling and tumefaction, owing to its infiltration with inflammatory exudate. The portion covering the hyaline cartilage of the navicular bone has lost its peculiar pearl-blue shimmer, and become a dirty yellow. Remembering that the bursal membrane 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.