The thorax is a division of an animal's body, that lies between the head and the abdomen.
In humans, the thorax is the region of the body that extends from the neck to the diaphragm, not including the upper limbs. The heart and the lungs reside in the thoracic cavity, as well as many blood vessels. This area is protected by the rib cage and the sternum.
Diagram of a tsetse fly, showing the head, thorax and abdomen..