2. In insects, the thorax is the middle of the three main sections of the body. The thorax also refers to similar areas on arachnids (insects with no spines) and crustaceans (mostly water-dwelling creatures with an outer skeleton, such as crabs and lobsters).

The plural of thorax is thoracis and thoraces. An adjective used to describe the area of the thorax is thoracic (also known as thoracal). Thoracic also means pertaining to the part of the vertebrae (bones that form an opening in which the spinal cord passes) that are in the area behind the thorax (see above for description). There are 12 thoracic vertebrae, known as T1 through T12. Thoracic is also known as thoracal. Thorax is Greek for "chest."

1. In humans, the thorax is another name for chest, the cage of bones and cartilage (a type of tissue) that extends from the bottom of the neck to a muscle known as the diaphragm, which separates it from the belly. The thorax protects important parts of the body, such as those that assist in breathing and pumping blood throughout the body. Important body parts covered by the thorax include the heart, lungs, and esophagus (the tube in the throat the food goes down). Large blood vessels such as the aorta and arteries of the lungs are covered by the thorax. The aorta is the largest artery of the body. An artery is a blood vessel that carries blood away from the heart.

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The front of thorax is made up of 12 ribs, the sternum (the flat bone in the middle of the chest), and cartilage that connects the ends of ribs with the sternum. The back of the thorax is made up of 12 bones that form an opening in which the spinal cord passes. In general, the thorax of a woman is smaller, has a shorter sternum (see above), and has more movable upper ribs than the sternum of a man.
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