The
medullary cavity (
medulla, innermost part) is the central cavity of
bone shafts where red
bone marrow and/or yellow bone marrow (
adipose tissue) is stored; hence, the medullary cavity is also known as the marrow cavity. Located in the main shaft (cortical bone) of a long bone (
diaphysis) (consisting mostly of
compact bone), the medullary cavity has walls composed of
spongy bone (cancellous bone) and is lined with a thin, vascular membrane (
endosteum). However, the medullary cavity is the area inside any bone (long, flat, etc.) that holds the bone marrow.