The function performed in the bone marrow, but not in the ossified bones of the skeleton, is hematopoiesis—the production of blood cells.
Bone marrow, particularly red bone marrow, is responsible for generating red blood cells (erythrocytes), white blood cells (leukocytes), and platelets (thrombocytes). This process is essential for oxygen transport, immune defense, and blood clotting.
In contrast, the ossified (hardened) bones primarily provide structural support, protection, movement, mineral storage, and leverage for muscles, but they do not produce blood cells.