Bones that do not contain red bone marrow in adults include bones such as the humerus, femur, tibia, and fibula. Physiologically, red bone marrow in the human body is generally found only in the proximal ends of short, flat, and long bones, as well as in such areas as the skull, ribs, ilium, and the proximal ends of the humerus and femur, where it is generally distributed, and elsewhere where it is generally not contained. Bone marrow is located within many of the bones of the body and is the body’s hematopoietic tissue. At the youngest stage of the human body, the bone marrow in the marrow cavity is generally red bone marrow, and as we grow older, the red bone marrow within the long bones is gradually replaced by adipose tissue to become yellow bone marrow. By adulthood, the entire long bone backbone of the body is almost full of yellow bone marrow. In normal adults, the proportion of red bone marrow and yellow bone marrow is equal. Bone marrow is the blood-forming organ of the human body, and red bone marrow has the function of hematopoiesis, while yellow bone marrow does not. The yellow marrow in the bone marrow cavity can also be converted to red marrow when there is a large amount of blood loss.