Microscopic images of joint cartilage from region of interest. (a) Rabbit MCP joint sections were stained with iron hematoxylin, safranin O, and fast green. This combination of stains identifies the uncalcified cartilage (red), calcified cartilage (dark red), and bone (blue-green). The tidemark (arrow) is apparent and marks the division between the uncalcified and calcified cartilage. (b) Unstained sections were imaged under polarized light microscopy. The superficial zone is indicated by the two arrows at the articular surface. The bracket encloses the mid zone, which due to the anisotropic arrangement of collagen fibers does not exhibit birefringence. Bars = 100 μm.