Each lung is conical in shape, and presents for examination, an apex, a base, and two surfaces.
The Apex forms a tapering cone which extends into the root of the neck about an inch and a half to two inches above the level of the top of the first rib.
The Base is broad and concave and rests upon the convex surface of the diaphragm, which separates the right lung from the upper surface of the right lobe of the liver and the left lung from the upper surface of the left lobe of the liver, the stomach, and spleen.
Surfaces.—There are two in number. The external, costal or thoracic surface is smooth, convex and corresponds to the form of the cavity of the chest. The inner or mediastinal surface is concave, and the middle portion, where all the vessels enter and leave the lung is called the root.
Lobes.—Each lung is divided up into lobes. The right lung has three lobes, and the left lung has two lobes.
Weight.—The weight of both lungs together is about 42 ounces, the right lung being a little heavier than the left. The lungs are heavier in the male than in the female. The male lungs weigh from 42 to 45 ounces, and the female lungs weigh from 32 to 35 ounces.
Color.—The color of the lungs at birth is a pinkish white, in adult life a dark slate color, mottled in patches and as age advances this mottling assumes a black color.
Substance.—The substance of the lung is of a light porous, spongy texture. It floats in water, if it has once been filled with air. It is elastic and for this reason we always find the lung collapsed after death.
The structure of the lung is such that the blood brought by the pulmonary artery comes into close relation with the air in the air-cells which enters from the bronchioles. The blood gives off carbon dioxide to the air-cells and the air in the cells furnishes oxygen for the blood. The process of respiration causes the dark blood brought from the heart by the pulmonary arteries to return to the heart as red blood in the pulmonary veins.
Arteries.—The bronchial arteries supply the lungs with nutrition.