(marrow) the tissue contained within the internal cavities of the bones. At birth, these cavities are filled entirely with blood-forming myeloid tissue (red marrow) but in later life the marrow in the limb bones is replaced by fat (yellow marrow). Samples of bone marrow may be obtained for examination by aspiration through a stout needle or by trephine biopsy. See also haemopoiesis.
Subjects: Medicine and Health.