The central shaft of a long tubular bone (e.g., tibia) lying between the epiphyses (the extremities of the bone). It is the first to ossify and contains an extended ossification centre (see figure below). It has a hollow middle (medullary cavity) containing bone marrow that is red in children, and which changes with age to fat-storing yellow marrow as less blood cell production is required (see figure below). Red marrow, found in the epiphyses as the end of long bones, forms red blood cells in mammals. In adults, it is mostly found in the flat bones of the skull, the ribs, the vertebrae and pelvic bones. Yellow marrow is simply a fat storage area. Usually, it does not produce any blood cells, but under certain adverse conditions (e.g., hemorrhage) it can assume this function. (plural: diaphyses).
