Final answer:
The proximal one-third of a long bone refers to the area near the proximal end and includes part of the tubular shaft known as the diaphysis, which is composed of dense and hard compact bone.
Step-by-step explanation:
When referring to the structure composed of bone in the proximal one-third, we are discussing the components of a long bone. A long bone is characterized by its diaphysis and epiphysis, where the diaphysis is the tubular shaft that runs between the proximal and distal ends. In the context of the question, the proximal one-third of the bone refers to the area near the proximal end and includes part of the diaphysis.
The diaphysis is composed of dense and hard compact bone. Examples of long bones include the femur, which is the longest and strongest bone in the body. The head of the femur is indicative of the proximal end, and this area is part of the proximal one-third referenced in the question.