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. Seeing that with every movement of the foot the perforans tendon is called upon to glide over this surface, it is clear that a secondary effect must be that of inducing erosion and destruction of the tendon. The point at which this usually commences is at the bottom of the depression that accommodates the ridge on the bone. With erosion of the cartilage and of the tendon at points exactly opposite each other, we have two surfaces come together that are prone to readily unite, and fibrous tissue adhesions often take place between the bone and the tendon. In some measure this accounts for the torn and ragged appearance of the tendon. Adhesions take place, and, under some small strain, are broken down. This may happen more than once or twice, and with each breaking of the adhesion between the bone and tendon, fibres from the latter are lacerated and torn from their place (see Fig. 162).