The thorax is a division of an animal's body that lies between the head and the abdomen. In mammals, the thorax is the region of the body formed by the sternum, the thoracic vertebrae and the ribs. It extends from the neck to the diaphragm, and doesn't include the upper limbs. The heart and the lungs reside in the thoracic cavity, as well as many blood vessels. The inner organs are protected by the rib cage and the sternum. In insects and the extinct trilobites, the thorax is one of the three m… (More on Thoracic)