Osteosarcomas are destructive tumors of bone. They slowly eat away at bone tissue destroying it in the process. While common in the dog and cat they are rare in other species. A cross section of the tumor is shown above. The normal musculature has been reflected away to show the mass. Note the dense appearing off white tissue. In Bucks case the tumor was slowly eating away at his lower jaw. In the process of doing so it had damaged his cranial nerves that are responsible for the muscle tone of the face. This explains why he presented with facial asymmetry.