In the thoracic cavity is a pair of lungs. Each lung is an individual organ containing the branching elements of one side of the respiratory tree, the connected alveoli, and the corresponding pulmonary NAVL.
As with the other organs, the tissues are held together with fibrous connective tissue
Located in the middle of the thorax, between the two pleural cavities, is the mediastinum ("I stand between"). The mediastinum is a tissue- and organ-filled space. Within it, the heart (of the blood circulatory system) is located at the same level as the lungs.
The two lungs occupy their respective sides of the thoracic cavity.
The left lung tends to be smaller. This makes room for the extension of the heart into the left side of the thorax.
In general, the right lung is divided into three major lobes. The left lung is in two major lobes.
Due to the branching pattern of the respiratory tree (and associated NAVL), each lung consists of broncho pulmonary segments--10 in the right lung and 8 in the left lung.