What structure is the site of bone growth in length?

The site of bone growth in length is primarily the epiphyseal plate, also known as the growth plate. This cartilage structure is located between the epiphysis and diaphysis of long bones and is responsible for the elongation of bones during childhood and adolescence. As new cartilage forms on the epiphyseal side, it is gradually replaced by bone on the diaphyseal side, allowing for continued growth until the plate eventually fuses in early adulthood.