CHAPTER VII
THE CREMATORY OF THE SYSTEM
The Organs of Respiration consist of the lungs and the air passages leading to them. The lungs are two in number, and occupy the pleural chamber of the thorax, one on each side of the median line, being separated from each other by the heart, the greater blood-vessels and the larger air tubes. Each lung is free in all directions, except at the root, which consists chiefly of the bronchi, arteries and veins connecting the lungs with the trachea and heart. The lungs are spongy and porous, and their tissues are very elastic. They are covered with a delicately constructed but strong sac, known as the pleural sac, one wall of which closely adheres to the lung, and the other to the inner wall of the chest, and which secretes a fluid which allows the inner surfaces of the walls to glide easily upon each other in the act of breathing.
The Air Passages consist of the interior of the nose, pharynx, larynx, windpipe or trachea, and the bronchial tubes. When we breathe, we draw in the air through the nose, in which it is warmed by contact with the mucous membrane, which is richly supplied with blood, and after it has passed through the pharynx and larynx it passes into the trachea or windpipe, which subdivides into numerous tubes called the bronchial tubes (bronchia), which, in turn, subdivide into and terminate in minute subdivisions
