Cortical bone can also be refered to as Compact bone. Cortical bone is found in the diaphysis of long bones and covers the Cancellous bone in flat, short and irregular bones. Cortical bone is made of Haversian (Osteonal) bone which are concentric circles of Lamellar bone approximately 200-300 um in diameter. These Haversion bone circles are formed side by side and create the diaphyseal shaft of long bones. The Periosteal (outer) layer of the diaphysis of a long bone is made of Circumferential Bone which are layers of lamellar bone. Haversian and Circumferential Bone are made of Lamellar bone but are arranged differently. Cortical bone is dense with low porosity. It is stiffer that Cancellous bone but less ductile.