NEW BONE is created in the human body in (1) fetal osteogenesis and postfetal bone growth, the repair of fractures, cysts and inflammations, arthrodeses and bone-grafting procedures, and (2) in heterotopic bone formation. The latter is found most commonly in muscles, fascia and tendons but also in such varied tissues as severely damaged eyes, meninges of the brain, tonsils, lungs, thyroid gland, ovaries, uterine tube, pelvis, kidneys, scars of wounds and walls of arteries (Table 1). The development of bone in so great a variety of tissues indicates a potential universality in its growth, especially within tissues of mesenchymal origin. Although there are many similarities between normal osteogenesis
and the heterotopic form, there is no sufficient evidence that these processes are identical. The first group represents manifestations of growth and regeneration in normal phylogenetic sites as contrasted with the second group of heterotopic bone formation which is extraskeletal. The common