What is the X in X-mas?
epiphysis e·piph·y·sis (ĭ-pĭf'ĭ-sĭs)
n. pl. e·piph·y·ses (-sēz')
The end of a long bone that is originally separated from the main bone by a layer of cartilage but that later becomes united to the main bone through ossification.
See pineal body.
expanded end of the long bones in animals, which ossifies separately from the bone shaft but becomes fixed to the shaft when full growth is attained. The epiphysis is made of spongy cancellous bone covered by a thin layer of compact bone. It is connected to the bone shaft by the epiphyseal cartilage, or growth plate, which aids in the growth of bone length and is eventually replaced by bone.