The bone is covered with a thin membrane called the periosteum. The main job of the periosteum is to make new bone for growth and repair. The center of most bone is hollow. A material called marrow fills this space. Red marrow produces red and white blood cells and platelets.
Yellow marrow contain a large amount of fat.
Cartilage is a type of connective tissue lacking minerals in the matrix. Its major function lies in its flexibility. The developing human skeleton contains large amounts of cartilage. As the baby develops the cartilage is replaced by bone. This process is called ossification.