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Thorax

2007 Schools Wikipedia Selection. Related subjects: General Biology

   Diagram of a tsetse fly, showing the head, thorax and abdomen
   Diagram of a tsetse fly, showing the head, thorax and abdomen

   The thorax is a division of an animal's body that lies between the head
   and the abdomen.

   In humans, the thorax is the region of the chest formed by the sternum,
   the thoracic vertebrae and the ribs. It extends from the neck to the
   diaphragm, not including the upper limbs. The heart and the lungs
   reside in the thoracic cavity, as well as many blood vessels. The inner
   organs are protected by the rib cage and the sternum.

   In insects and the extinct trilobites, the thorax is one of the three
   main divisions (or tagmata) of the creature's body, each of which is in
   turn composed of multiple segments. It is the area where the wings and
   legs attach in insects, or an area of multiple articulating plates in
   trilobites. In most insects, the thorax itself is composed of three
   segments; the prothorax, the mesothorax, and the metathorax. In extant
   insects, the prothorax never has wings, though legs are always present
   in adults; wings (when present) are restricted to at least the
   mesothorax, and typically also the metathorax, though the wings may be
   reduced or modified on either or both segments (as in the fly shown,
   where the metathoracic wings have been reduced to tiny balancing organs
   called halteres). In the Apocritan Hymenoptera, the first abdominal
   segment is fused to the metathorax, where it forms a structure known as
   the propodeum. Accordingly, in these insects, the functional thorax is
   composed of four segments, and is therefore typically called the
   mesosoma to distinguish it from the "thorax" of other insects.

   Each thoracic segment in insects is further subdivided into various
   parts, the most significant of which are the dorsal portion (the
   notum), the lateral portion (the pleuron; one on each side), and the
   ventral portion (the sternum). In some insects, each of these parts is
   composed of one to several independent exoskeletal plates with membrane
   between them (called sclerites), though in many cases the sclerites are
   fused to various degrees.
   The trilobite body is divided into three major sections, a cephalon
   with eyes, mouthparts and sensory organs such as antennae, a thorax of
   multiple similar segments (that in some species allowed them to roll up
   into a ball), and a pygidium, or tail section. © Sam Gon III
   The trilobite body is divided into three major sections, a cephalon
   with eyes, mouthparts and sensory organs such as antennae, a thorax of
   multiple similar segments (that in some species allowed them to roll up
   into a ball), and a pygidium, or tail section.

                               © Sam Gon III

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