ETYM Latin, from Greek.
The part of the human body between the neck and the diaphragm or the corresponding part in other vertebrates; SYN. chest, pectus.
In tetrapod vertebrates, the part of the body containing the heart and lungs, and protected by the rib cage; in arthropods, the middle part of the body, between the head and abdomen.
In mammals the thorax is separated from the abdomen by the muscular diaphragm.
Cavity between neck and abdomen, containing lungs, heart, etc.; chest.

1. Part of an insect's body that bears the wings and legs.
2. The middle region of the body of an arthropod between the head and the abdomen; in insects it bears the true legs and wings.
3. In insects the thorax bears the legs and wings. The thorax of spiders and crustaceans is fused with the head, to form the cephalothorax.