<P> The growth in diameter of bones around the diaphysis occurs by deposition of bone beneath the periosteum . Osteoclasts in the interior cavity continue to resorb bone until its ultimate thickness is achieved, at which point the rate of formation on the outside and degradation from the inside is constant . </P> <P> During endochondral ossification, five distinct zones can be seen at the light - microscope level . </P> <Table> <Tr> <Th> Name </Th> <Th> Definition </Th> </Tr> <Tr> <Td> Zone of resting cartilage </Td> <Td> This zone contains normal, resting hyaline cartilage . </Td> </Tr> <Tr> <Td> Zone of proliferation / cell columns </Td> <Td> In this zone, chondrocytes undergo rapid mitosis, forming distinctive looking stacks . </Td> </Tr> <Tr> <Td> Zone of maturation / hypertrophy </Td> <Td> In this zone, the chondrocytes undergo hypertrophy (become enlarged). Chondrocytes contain large amounts of glycogen and begin to secrete alkaline phosphatase . </Td> </Tr> <Tr> <Td> Zone of calcification </Td> <Td> In this zone, chondrocytes are either dying or dead, leaving cavities that will later become invaded by bone - forming cells . Chondrocytes here die when they can no longer receive nutrients or eliminate wastes via diffusion . This is because the calcified matrix is much less hydrated than hyaline cartilage . </Td> </Tr> <Tr> <Td> Zone of ossification </Td> <Td> Osteoprogenitor cells invade the area and differentiate into osteoblasts, which elaborate matrix that becomes calcified on the surface of calcified cartilage . This is followed by resorption of the calcified cartilage / calcified bone complex . </Td> </Tr> </Table> <Tr> <Th> Name </Th> <Th> Definition </Th> </Tr>

Where is bone added to during endochondral ossification