Lung

Collier's New Encyclopedia (1921)

an organ of respiration. Human Anatomy. The organs of respiration are on each side of the chest, conical, and separated from each other by the heart in front and a membranous partition, the mediastinum. Externally they are convex, to correspond with the chest walls, and internally concave to in a tapering cone and below in a broad receive the heart; above they terminate concavity resting on the diaphragm. In color they are mottled, pinkish-gray, speckled with black. Each is divided into two lobes, separated by a deep fissure, and the right lung has a third lobe above of triangular shape; the right is also larger on account of the heart lying toward the left side. The lungs are kept in position by their roots, composed of the bronchi, pulmonary artery, and pulmonary veins; the right side presents the bronchus above, then the artery, then the veins; but on the left side we find the bronchus between the artery and the veins. Each lung is inclosed in a serous membrane, the pleura, which extends to its root, and is then expanded on the chest wall. The lungs are composed of minute ramifications of the bronchial tubes, terminating in intercellular passages and quadrilateral or hexaggonal air-cells, along with ramifications of the pulmonary artery and veins, bronchial arteries and veins, lymphatics and areolo-fibrous tissue constituting the nerves, the whole bound together by parenchyma of the lungs. See PHYSI- OLOGY: RESPIRATION. salient angle to Comparative Anatomy. - In the lowest and simplest forms of animal life (aquatic), we find no trace of respiratory organs, the interchange between the layer of water with the aerating surface being effected by the general movement of the body, or by cilia. In most of the Mollusca we find gills in the place of lungs, except in the terrestrial species, as the snail or slug, where we have a lung which is a simple cavity in southern constellations. It is situated the back communicating directly with between Centaurus and Ara, just under the air, and covered with minute bloodvessels; in bivalve mollusks again, as in the oyster, it is the internal surface of the mantle or skin-lining which is the special organ, with the same essential structure as gills. In the Articulata, as tapeworm, marine worms, Crustacea, as the crab tribe, we find a somewhat similar arrangement to that of the Mollusca, but in insects, insects, and other proper air-breathing Articulata, we have a reg ular series of air-sacs along each side of the body, opening by pores, called spiracles or stigmata, so in the spider-tribe, but in a more concentrated form, and more resembling the lung of the Vertebrata. The gills of fishes come next in the scale, accompanied in many cases with an air bladder, especially in those approaching the Reptilia in their organization, and in some of these it is a double sac, the analogue of the double lung. The lungs of the reptiles are, for the most part, capacious sacs occupying a good deal of the trunk cavity, ty, but not filled, like those of the Mammalia, by an act of inspiration, but chiefly by the process of swallowing. In birds we have the connecting link between the types of structure in the two classes. Pathology. There are various diseases of the lungs; two of the most important are tubercular phthisis and pneumonia.