MINERALISATION OF HYALINE CARTILAGE IN THE SMALL-SPOTTED DOGFISH

A b s t r a c t The cartilaginous skeleton of the selachian fish Scyliorhinus canicula L. was studied with special emphasis on matrix mineralisation. Calcification of cartilage matrix in selachians neither initiates cartilage destruction nor precedes removal of cartilage, as is the case in mammals. X-ray examination revealed superficially located mineral deposits (cortical calcification, “Rindenverkalkung“) in almost all pieces of hyaline cartilage. In vertebrae, additional mineral deposits concentrically embraced the notochord and were seen in lateral segments of the neural arch. Microscopically, hyaline cartilage was inconspicuous besides inorganic deposits in a distinct, 15–45 µm thick band of mineralisation parallel to the cartilage surface. This mineralised area was separated from the perichondrium by an interposed, 20–30 µm thick layer of regularly built cartilage. Calcium carbonate and phosphate were identified histochemically. Organic matrix in mineralised areas showed increased binding of hematoxylin and Periodic acid-Schiff reactivity. Basophilia, metachromasia, and alcianophilia were reduced, and stain-ing with acid fuchsin was prominent. Immunostaining showed significant amounts of keratan sulphate and some collagen type I to substitute for collagen type II. Chondrocytes in mineralised matrix were intact or showed nuclear pyknosis and cellular disintegration. Immunostaining for non-collagenou