Antigen - a molecule that the immune system recognizes as part of the body or foreign to the body. Appendicular skeleton - a part of the skeleton composed of 126 bones found in the flexible regions of the body, including shoulders, hips and limbs. Axial skeleton - the central, anchoring part of the bony skeleton that consists of the skull, backbone (vertebrae) and rib cage. Bile - a chemical produced by the liver and stored temporarily in the gall bladder that is released into the intestines to help in fat digestion.