The thoracic cage encloses and protects the heart, lungs, and some abdominal organs. It also supports the bones of the shoulder girdle and arm.
Fibroblasts and collagen work together in the body to heal bone breaks. 1 = Marrow; 2 = Cortical bone; 3 = Periosteum; 4 = Osteocyte; 5 = Collagen; 6 = Fibroblast; 7 = Neovascularization organizing blood clot; 8 = Dead cortex (empty lacunae); 9 = Live cortex. (From Rubin, E., M.D., and Farber, J. L., M.D. Pathology. 3rd Ed. Philadelphia: Lippincott, Williams & Wilkins, 1999.)