Red marrow is found mainly in the flat bones - like the hip bone, breast bone, skull, ribs, vertebra (the bones that make up the spinal column), and shoulder blades - and in the cancellous ("spongy") material at the ends of the long bones like the femur (thigh bone) and humerus (upper forearm bone). Yellow marrow is found inside the hollow middle section, or medullary cavity of the long bones.