The Left Bronchus.—The left bronchus is smaller and longer than the right. It is two inches in length and enters the lung at a point opposite the body of the sixth dorsal vertebra.
Each bronchus divides into smaller divisions called bronchial tubes.
Each bronchial tube divides into still smaller divisions called bronchioles.
Each bronchiole ends in the air cell.
The Pleurae.
—Each lung is invested upon its external surface by an exceedingly delicate serous membrane, the pleura. This encloses the organ as far as its root, and is then reflected upon the inner surface of the thorax.
The pulmonary pleura is the portion investing the surface of the lung, and dipping into the fissures between its lobes.
The parietal pleura is that which lines the inner surface of the chest.
The space between these two layers is called the cavity of the pleurae, (the pleural cavity); and contains nothing but a very little clear fluid.
In the healthy condition the two layers are in contact and there is no real cavity, but after death the lungs become collapsed and separate from the walls of the chest. Each pleura is therefore a shut sac, one occupying the right, and the other the left half of the thorax, and they are perfectly separated from one another. The two pleurae do not meet in the middle line of the chest, excepting for a short distance between the second and third pieces of the sternum—a space being left between them, which contains all the viscera of the thorax excepting the lungs; this is called the mediastinum.