Spongy bone can also be found in the rib slide (21).   It contains large marrow spaces defined by shelves and spicules of bone. The inner space is lined by osteoblasts and osteoclasts (called the endosteum). Osteocytes can be seen in layers in adult spongy bone. Outside all of bone, is a connective tissue sheath called the periosteum.  It contains inner layers of osteogenic cells that can give rise to osteoblasts and make new bone.