Endochondral Bones: form from a hyaline cartilage model, most bones in skeleton fall under this category, cartilage first broken down in the diaphysis & progressively replaced w/ bone while periosteum develops on outside, band of hyaline cartilage ( epiphyseal plate) remains between epiphysis & diaphysis, layers of cartilage cells undergoing mitosis make up plate where bones lengthen, osteoclasts break down calcified matrix, osteoblasts deposit bone in place of calcified cartilage, long bone continues to lengthen while cartilaginous cells of epiphyseal plate are active, as compact bone deposits, medullary cavity forms in diaphysis, which eventually fills w/ yellow bone marrow