Final answer:
The medullary cavity is a hollow region in long bones filled with yellow marrow. It is involved in bone growth, repair, and remodeling.
Step-by-step explanation:
The medullary cavity is a hollow region found in the diaphysis (or shaft) of long bones. It is filled with yellow marrow, which is mainly composed of fat cells. The medullary cavity is involved in the process of bone growth, repair, and remodeling. It has a delicate lining called the endosteum, where these processes occur. The outer surface of the bone is covered with a membrane called the periosteum, which contains blood vessels, nerves, and attaches tendons and ligaments to bones.