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body division found in certain animals. In humans and other mammals it lies between the neck and abdomen and is also called the chest. The skeletal frame of the thorax is formed by the sternum (breastbone) and ribs in front and the dorsal vertebrae in back. Within the thoracic cavity are the heart, lungs, and esophagus. The chest and abdominal cavities are separated by a muscular structure, the diaphragm. In insects and other arthropods the thorax is a body division consisting of several segments lying between the head and abdomen, to which are attached legs or other appendages.



the upper (in humans) or anterior (in most vertebrates) part of the trunk.

The shape of the thorax is determined by its skeleton—the chest and pectoral girdle—and by the muscles arranged on its surface. In arthropods the thorax is the section between the head and the abdomen. In primitive crustaceans (for example, Phyllopoda) the segments of the thorax are numerous and not constant in number; they bear nonspecialized appendages, equipped simultaneously for swimming, chewing, and breathing (gills). In higher crustaceans the number of segments of the thorax is reduced to between four and eight and becomes constant; part of the segments fuse with the head and their appendages become maxillipedary. In Arachnida and Xiphosura the segments of the thorax bear four pairs of gressorial legs and are usually merged with the head into a cephalothorax. In insects the thorax consists of three segments (prothorax, mesothorax, and metathorax), to each of which is attached a pair of legs; in higher insects one pair of wings each is attached to the mesothorax and metathorax in the adult stage.


The chest; the cavity of the mammalian body between the neck and the diaphragm, containing the heart, lungs, and mediastinal structures. Also known as thoracic cavity.
(invertebrate zoology)
The middle of three principal divisions of the body of certain classes of arthropods.


1. the part of the human body enclosed by the ribs
2. the corresponding part in other vertebrates
3. the part of an insect's body between the head and abdomen, which bears the wings and legs
References in periodicals archive ?
C[O.sub.2] insufflation to the bilateral thoraxes per se has the potential risk of hypoxia because of forced restriction of dependent lung expansion due to partial collapse of the distal trachea and bronchus.
When the body parts were analyzed separately, the females' and males' iron concentrations found were 224 and 114 ppm in the heads, 73 and 42 ppm in the thoraxes, 25 and 52 ppm in the abdomens, and 81 and 63 ppm in the wings, respectively.
Figure 2, which shows the interaction of body parts and species, shows that: 1) on average, swallowtails have higher iron concentrations than monarchs; 2) on average, there are higher iron concentrations in butterfly heads than in the other three body parts; and 3) swallowtails have higher iron concentrations in their heads and wings than monarchs, while iron levels in thoraxes and abdomens are similar in the two species.