n. [ Cephalo- + thorax. ] (Zool.) The anterior portion of any one of the Arachnida and higher Crustacea, consisting of the united head and thorax. [ 1913 Webster ]

n. [ Endo- + thorax. ] (Zoöl.) An internal process of the sternal plates in the thorax of insects. [ 1913 Webster ]

n. [ Ento- + thorax. ] (Zoöl.) See Endothorax. [ 1913 Webster ]

n. Same as Hemothorax. [ 1913 Webster ]

n. [ NL. See Hemo-, and Thorax. ] (Med.) An effusion of blood into the cavity of the pleura. [ 1913 Webster ]

n. [ Hydro-, 1 + thorax. ] (Med.) An accumulation of serous fluid in the cavity of the chest. [ 1913 Webster ]

n. [ Meso- + thorax: cf. F. mésothorax. ] (Zool.) The middle segment of the thorax in insects. See Illust. of Coleoptera. [ 1913 Webster ]

n. [ NL.: cf. F. métathorax. See Meta-, and Thorax. ] (Zool.) The last or posterior segment of the thorax in insects. See Illust. of Coleoptera. [ 1913 Webster ]

n. [ Pneumato- + thorax. ] (Med.) See Pneumothorax. [ 1913 Webster ]

n. [ Gr. &unr_; air + E. thorax. ] (Med.) A condition in which air or other gas is present in the cavity of the chest; -- called also pneumatothorax. [ 1913 Webster ]

n. [ Pref. pro- + thorax. ] (Zool.) The first or anterior segment of the thorax in insects. See Illusts. of Butterfly and Coleoptera. [ 1913 Webster ]

n. [ Gr. &unr_; pus + E. pneumothorax. ] (Med.) Accumulation of air, or other gas, and of pus, in the pleural cavity. [ 1913 Webster ]

n. [ L., fr. Gr. &unr_;. ] 1. (Anat.) The part of the trunk between the neck and the abdomen, containing that part of the body cavity the walls of which are supported by the dorsal vertebrae, the ribs, and the sternum, and which the heart and lungs are situated; the chest. [ 1913 Webster ]

☞ In mammals the thoracic cavity is completely separated from the abdominal by the diaphragm, but in birds and many reptiles the separation is incomplete, while in other reptiles, and in amphibians and fishes, there is no marked separation and no true thorax. [ 1913 Webster ]

2. (Zool.) (a) The middle region of the body of an insect, or that region which bears the legs and wings. It is composed of three united somites, each of which is composed of several distinct parts. See Illust. in Appendix. and Illust. of Coleoptera. (b) The second, or middle, region of the body of a crustacean, arachnid, or other articulate animal. In the case of decapod Crustacea, some writers include under the term thorax only the three segments bearing the maxillipeds; others include also the five segments bearing the legs. See Illust. in Appendix. [ 1913 Webster ]

3. (Antiq.) A breastplate, cuirass, or corselet; especially, the breastplate worn by the ancient Greeks. [ 1913 Webster ]