Which structure is indicated by the blue arrow in the diagram?

Which structure is indicated by the blue arrow in the diagram?

• A. Medullary Cavity
• B. Yellow Marrow
• C. Endosteum
• D. Periosteum

Answer: (A)

The blue arrow is pointing to the hollow interior running through the shaft of a long bone—the medullary cavity. This central cavity stores marrow and is the space inside the diaphysis. In adults it’s typically filled with yellow marrow (fat), while the inner lining of that cavity is the endosteum and the outer covering is the periosteum. So the arrow indicates the medullary cavity itself, not the marrow, the inner lining, or the outer surface.

The blue arrow is pointing to the hollow interior running through the shaft of a long bone—the medullary cavity. This central cavity stores marrow and is the space inside the diaphysis. In adults it’s typically filled with yellow marrow (fat), while the inner lining of that cavity is the endosteum and the outer covering is the periosteum. So the arrow indicates the medullary cavity itself, not the marrow, the inner lining, or the outer surface.