And this is basically the innermost portion of our cell. Now this small layer that basically lines the innermost portion is our endosteum. The endosteum is basically a covering of the innermost portion of the bone. Now, right next to our medullary cavity we have this white portion shown by this section here that basically goes around the bone in both directions. This is known as our compact bone and the compact bone is also known as the cortical bone. This is a very dense and a very heavy portion of the bone.