Final answer:
The presence of an epiphyseal line in a bone signifies that the bone's longitudinal growth has ceased, typically occurring when an individual reaches early adulthood. This line is the remnant of what once was the epiphyseal plate, which previously allowed the bone to grow in length.
Step-by-step explanation:
The formation of an epiphyseal line indicates that the bone has likely stopped growing. During the growth phase of long bones, the epiphyseal plate is present and responsible for longitudinal bone growth. As a person reaches early adulthood, longitudinal growth comes to a halt as the cartilage in the epiphyseal plates ceases proliferation and is entirely replaced by bone, leaving behind the epiphyseal line. This signifies that the growth plate has been converted into bone, and the bone has reached its mature length.
Additionally, while the lengthening of the bone is restricted after the formation of the epiphyseal line, bones may continue to grow in diameter through appositional growth. This involves the resorption of old bone and the formation of new bone tissue, contributing to the increase in the bone's diameter.