Final answer:
When a bone is fully ossified, the epiphyseal plate is replaced by an epiphyseal line, indicating the end of lengthwise bone growth and skeletal maturity.
Step-by-step explanation:
When the bone is fully ossified, the visibility of the epiphysis changes as the epiphyseal plate is replaced by an epiphyseal line. This change is a hallmark of skeletal development and signifies that the bone has reached its full length and growth has ceased. During the process of endochondral ossification, secondary ossification centers form in the epiphyses, leading to the conversion of hyaline cartilage into spongy bone. This process continues until the skeleton reaches maturity, which typically occurs around the age of 20.
In the last stages of bone growth during adolescence, the epiphyseal plates close and are replaced by bone, forming the epiphyseal line. This signifies the end of the bone's growth in length. Thus, the transition from an epiphyseal plate to an epiphyseal line indicates that the individual has reached skeletal maturity and no additional growth in bone length can occur.