Fig. 2.

Ossification of appendicular long bones: Post-embryonic ossification of the limb in salamanders involves an endochondral and periosteal ossification, degradation of cartilage anlage and formation of a marrow cavity (m.c.) filled with adipocytes. Ossification has been associated with an animal's size; however, elements are not fully ossified as epiphyseal cartilage remains throughout the salamander life cycle. The participation of hypertrophic chondrocytes in ossification has been proposed and the presence of hypertrophic chondrocytes expressing osteogenic markers has been demonstrated (Chondro-osseous cells). Finally, the cartilage presents a loose organisation, but various zones can be identified, i.e. periarticular, resting, proliferative and hypertrophic zones. Other features of salamander appendicular elements include the erosion bay (e.b.), medullary trabeculae (m.t.) and Katschenko's line (K.t.).