The thoracic cavity is the cavity enclosed by the thorax, the upper thoracic opening and the diaphragm. The thorax is composed of the sternum, thoracic vertebrae, ribs and rib cartilage, and contains very important organs and tissues such as the heart, lungs, trachea, bronchi, thymus and large blood vessels. The thorax plays a very important role in protecting the organs and tissues in the thoracic cavity, and the rise and fall of the thorax facilitates the completion of the respiratory movement of the lungs. The upper boundary of the thoracic cavity is the upper thoracic orifice and the lower boundary of the thorax is the diaphragm. The diaphragm divides the trunk of the body into two parts, the upper part is called the thoracic cavity and the lower part is called the abdominal cavity. In short, the thoracic cavity refers to the cavity enclosed by the upper thoracic opening, the thorax and the diaphragm. The thoracic cavity is located below the neck, above the diaphragm, and in the upper part of the torso within the thorax.