tho·rax / ˈ[unvoicedth]ôrˌaks/ • n. (pl. tho·rax·es or tho·ra·ces / ˈ[unvoicedth]ôrəˌsēz/ ) Anat. & Zool. the part of the body of a mammal between the neck and the abdomen, including the cavity enclosed by the ribs, breastbone, and dorsal vertebrae, and containing the chief organs of circulation and respiration; the chest. ∎  Zool. the corresponding part of a bird, reptile, amphibian, or fish. ∎  Entomol. the middle section of the body of an insect, between the head and the abdomen, bearing the legs and wings.

thorax The anterior region of the body trunk of animals. In vertebrates it contains the heart and lungs within the rib cage. It is particularly well-defined in mammals, being separated from the abdomen by the diaphragm. In insects the thorax is divided into an anterior prothorax, a middle mesothorax, and a posterior metathorax, each of which bears a pair of legs; the hindmost two segments also both carry a pair of wings. In other arthropods, especially crustaceans and arachnids, the thorax is fused with the head to form a cephalothorax.

thorax The three segments of the body of an arthropod (Arthropoda) that lie between the head and the abdomen. Each thoracic segment carries a pair of legs. The three thoracic segments are termed the prothorax, mesothorax, and metathorax. In insects (Insecta), the mesothorax and metathorax may each carry a pair of wings. See TRILOBITOMORPHA.

thorax
1. The anterior portion of the body of an animal. In vertebrates it contains the heart and lungs and is separated by the diaphragm from the abdomen.

2. The three segments of the body of an insect that lie between the head and the abdomen. Each thoracic segment carries a pair of legs. The three thoracic segments are termed the prothorax, mesothorax, and metathorax. The mesothorax and metathorax may each carry a pair of wings.

thorax (thor-aks) n. the chest: the part of the body cavity between the neck and the diaphragm. The skeleton of the thorax is formed by the sternum, costal cartilages, ribs, and thoracic vertebrae. It encloses the lungs, heart, oesophagus, and associated structures. Compare abdomen.
—thoracic adj.