<Tr> <Th> FMA </Th> <Td> 9608 </Td> </Tr> <Tr> <Td_colspan="2"> Anatomical terminology (edit on Wikidata) </Td> </Tr> <P> Bone marrow is a semi-solid tissue which may be found within the spongy or cancellous portions of bones . In birds and mammals, bone marrow is the primary site of new blood cell production or hematopoiesis . It is composed of hematopoietic cells, marrow adipose tissue, and supportive stromal cells . In adult humans, bone marrow is primarily located in the ribs, vertebrae, sternum, and bones of the pelvis . On average, bone marrow constitutes 4% of the total body mass of humans; in an adult having 65 kilograms of mass (143 lb), bone marrow typically accounts for approximately 2.6 kilograms (5.7 lb). </P> <P> Human marrow produces approximately 500 billion blood cells per day, which join the systemic circulation via permeable vasculature sinusoids within the medullary cavity . All types of hematopoietic cells, including both myeloid and lymphoid lineages, are created in bone marrow; however, lymphoid cells must migrate to other lymphoid organs (e.g. thymus) in order to complete maturation . </P>

Blood cell production occurs in what section of the bone