Thorax definitions and example sentences on Wordnik

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American Heritage Dictionary (3)

noun The part of the human body between the neck and the diaphragm, partially encased by the ribs and containing the heart and lungs; the chest.
noun A part in other vertebrates that corresponds to the human thorax.
noun The second or middle region of the body of an arthropod, between the head and the abdomen, in insects bearing the true legs and wings.

Century Dictionary (7)

In anatomy and zoology, a part of the trunk between the head or neck and the abdomen or tail, in any way distinguished, as by containing the heart and lungs, by being inclosed with large ribs, or by bearing certain limbs not borne elsewhere. The name is applied both to the walls and to the cavity of this part of the body, but not to the contents of the cavity, and properly not to the thoracic appendages. In all vertebrates the thorax represents several of the segments or somites of the body succeeding the cervical and succeeded by the abdominal or pelvic segments. It is generally defined by the elongation of several ribs and the connection of some or most of these with a breast-bone, the thoracic skeleton thusforming a bony cage or frame which contains and defends the principal organs of circulation and respiration. In invertebrates, however, the thorax is defined upon other considerations. In man and all mammals the thorax is sharply marked off from the rest of the trunk by the lack of developed cervical and lumbar ribs, and its cavity is completely shut off from that of the abdomen by the diaphragm. The human thorax is of conical figure, somewhat like the frustum of a cone, narrowed above, broad below, of greater width than depth, and in cross-section somewhat cardiform or heart-shaped, from the intrusion of the backbone. Its truncated apex presents to the neck; its concave base is formed by the diaphragm. The cavity is divided into a pair of large pleural cavities, right and left, for the lungs, and a third submedian pericardial cavity for the heart. Where the opposite pleural cavities do not quite meet and fit, both before and behind, is an interpleural space, the anterior and posterior mediastinal cavity, or premediastinum and post-mediastinum. Besides the heart and lungs and their respective serous sacs (pericardium and pleura), the thorax contains many other structures, as the thoracic duct and thoracic aorta, many branches of the latter, etc. The thorax of other mammals differs from that of man chiefly in size, shape, degree of movability, etc., but not in actual structure or office. In birds the thorax is relatively very capacious and expansive. The sternum is of enormous size; long ribs frequently extend into the sacral region, and others, shorter, into the cervical region, so that the thorax encroaches in both directions. Its cavity is not shut off from that of the abdomen by any diaphragm. The ribs have a movable joint between their vertebral and sternal parts, contributing to the expansibility of the chest. Most of the abdominal as well as proper thoracic viscera are actually inclosed by the thoracic walls. See cut under epipleura. In those reptiles and batrachians which have breast-bones a thorax is distinguished much as it is in higher vertebrates. In serpents, which have no sternum, and whose ribs extend from head to tail, there is no distinction between thorax and abdomen; and the case is similar with turtles. In a few reptiles the thorax develops wing-like parachutes serving for a kind of flight. In fishes a thorax, or a thoracabdominal region, is usually well marked by long ribs from a postanal solid and fleshy part of the body, but there is no distinction of thoracic and abdominal cavities. The thorax may bear the pectoral fins, or these and the ventrals, or neither.
In entomology, that part of the body which is situated between the head and the abdomen, and in adult insects alone bears the wings and legs, when there are any. In the typical or hexapod insects the thorax is almost always a well-marked region, distinguished from the head in front and from the abdomen behind by bearing the only locomotory appendages which these insects possess in the adult state—namely, one or two pairs of wings and three pairs of legs. The thorax typically consists of three segments or somites of the body, one to each pair of legs, respectively named, from before backward, the prothorax, the mesothorax, and the metathorax, or sometimes the prethorax, medithorax, and post-thorax. The hard crust of each of these segments may and normally does consist of a number of pieces or individual sclerites, on the dorsal or tergal, on the lateral or pleural, and on the ventral or sternal aspects. These sclerites are known as tergites, pleurites, and sternites; they have also other names, and many of the individual sclerites have specific designations. Thus, dorsal sclerites or parts of each segment may be known as pronotum, mesonotum, and metanotum, and so with pleural and sternal sclerites of each thoracic segment. (See sclerite, and cuts under mesothorax and metathorax.) In ordinary descriptive entomology the name thorax has two special restrictions: (1) to the pronotum of coleopterous, hemipterous, and orthopterous insects; and (2) to the large mesothorax of dipterous insects (see thoraciform).
In Crustacea and Arachnida, a part of the body in advance of and in any way distinguished from the abdomen or tail, but usually blended with the head to form a cephalothorax. In ordinary arachnidans, as spiders, and in the higher crustaceans, as crabs, lobsters, shrimps, prawns, and crawfishes, several segments of the body are more or less completely fused in one mass; and the limbs are often so gradually metamorphosed into mouth-parts that even these indicia fail to discriminate a thorax from the head in every case. Generally, however, the bearing of eight or ten legs, developed as ambulatory organs, serves to denote a thorax. In many or most of the lower or entomostracous crustaceans a thorax is indistinguishable from the abdomen as well as from the head, and the character of its appendages does not always decide the case. See Decapoda, Tetradecapoda, Thoracipoda, thoracetron.

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The thorax, which is also known as the middle body segment includes wings and six jointed legs.
Pneumo-thorax will be the result of either lesion; and by the accumulation of air in the pleura the lung will suffer pressure. — Surgical Anatomy
Note the strong thorax which is filled with muscles to operate the wings in flight. — An Elementary Study of Insects
The curious suggestion of the thorn is produced not only by the outline, but by the curious fact that the hopper never sits across the twig, but always in the direction of its length; and, what is more, the projecting point of the thorax is always directed towards the end of the branch, or direction of growth. — My Studio Neighbors
This is called the thorax, which means chest. — Little Busybodies The Life of Crickets, Ants, Bees, Beetles, and Other Busybodies

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