Light micrograph of a developing finger bone in a late fetus. At the top is a joint cavity where the medial phalange is articulating with the proximal phalange. The heads of the two long bones, the epiphyses, consist entirely of cartilage at this stage of development. Mixed spicules consisting of bone and cartilage are seen in the marrow portion of the bone. Bone tissue, stained dark blue, is also present in the diaphysis of the bone. Mallory-Azan stain. Magnification: x45.