Fig. 1

Cartilage mineralization in the growing antler of white-tailed deer. (A) Initiation of mineralization. Individual foci of mineralization (solid arrow) appear in the perilacunar matrix. Mineralization foci grow and coalesce (open arrow). Continued growth (star) encircles the chondrocytes until encirclement with mineral is complete (double star). Mineralization begins in mid-trabecular and spreads toward trabecular margins. (B) Mineralization of cartilage trabeculae. Mineralization foci have grown until almost all of the cartilaginous spicule contains mineral (A and B, after Banks and Newbrey, 1982a; reproduced with the permission of the publisher). C and D. Ultrastructure of chondrocytes in the calcification zone. (C) The calcification appears as discrete radial foci (arrows) that surrounds the cells. Eventually, these foci will fuse to form a mineralized sphere completely surrounding the cells. (D) Higher magnification of matrix vesicles in the early calcification zone. The first hydroxyapatite crystals are seen on the surface of matrix vesicles (dark arrow). Inset: a calcified site, at the centre there is a matrix vesicle (large open arrow) and many condensed ruthenium red (RR) granules immediately surrounding the vesicle (C and D, after Newbrey and Banks, 1982b; reproduced with the permission of the publisher). E and F. Ultrastructure of matrix vesicle. (E) The matrix vesicle in the antler cartilage, residing in the centre of a condensed accumulation of RR-positive proteoglycan granules (arrows). (F) The matrix vesicle in the rat growth plate cartilage. A centralized matrix vesicle and surrounding proteoglycan granules (small arrows) are apparent. A lamina limitans (large arrows) surrounds the perimeter of the matrix vesicle. (E and F, after Banks and Newbrey, 1982b; reproduced with the permission of the publisher)