THE LUNGS (rye4pwv, Gr. ; Pulmo, Lat.; Pounton, Fr.; Lungen, Germ. ; Lungs or Lights, Engl.) coincide typically in structure with the compound grape-like glands. The lobules and air-cells constitute the glandular paren chyma. The larynx, trachea and bronchi represent the excretory apparatus. They differ from all other glands, however, in the mechanism of their action. They simultane ously eliminate and absorb. In the lungs two diametrically opposed functions proceed in the same place at the same tirne. This mechanical paradox occurs in the example of no other gland. Secretion and excretion are successive steps of the same process. They are not contrary functions. The whole mass of the blood passes through the lungs : other glands receive only a part. The air-passages and cells are far more capacious than the corresponding parts of other glands. This characteristic results frorn the aeriform nature of the compounds emitted and received. Aeriform bodies are subject to rapid varia tions of bulk ; fluids undergo no material changes of volume, through fluctuations of temperature ; thence, .in the instance of the lungs, results the necessity for mechanical pro visions, which in ordinary glands would exist to no purpose. The elastic tissue and resilient cartilages so abundantly introduced into the structure of the air-passages and cells realise the required provision. The excretory ducts of all other glands are membranous, the opposite sides of which are capable of collapsing into contact. Fluid in motion readily forces its way through a collapsed tube : air can only traverse a patulous channel.
In man the lungs are two in number. They are contained in the cavity of the thorax, one on either side of the spine, and embraced by, but still exterior to the pleura. The pleura pulmonalis and pleura parietalis are everywhere and always in actual contact. It follows that the space of the thorax must be at all times perfectly filled by the lungs and other organs. In figure each lung is conical. The right is wider and shorter than the left, a difference which results from the position of the liver on the right side and the heart on the left. The right lung is cut by deep fissures into three lobes ; the left only into two. The
base of each lung presents downwards, and rests on the diaphragm ; that of the right is more concave than that of the left. On the right side the liver bulges upwards, encroach ing upon the chest. The anterior edge of the right lung slopes off obliquely downwards and backwards, so that it projects much lower by its posterior than by its anterior border. On the left side the heart occupies the space which, in the absence from this place of this organ, might have been engaged by a third lobe.
The apices of the lungs project above the level of the first rib. The right is higher than the left. The dorsal aspect of the lungs, thick, round, and vertical, is received into the hollow of the ribs near the vertebrm.
It is longer than the anterior. The posterior and inferior margins descend into thc angular space between the ribs and the diaphragm. The anterior border is thin, irregular, and oblique. That of the left extends forwards over the pericardium. The inner surface of each lung presents towards the mediastinum,. That of the left is hollowed out to receive the heart. The root of each lung is attached to the posterior edge of its inner surface. Each lung is divided into lobes by fissures, which commence near the apices, and descend ob liquely forwards, to end in the anterior border near the base. The fissure divides the lung, on either side, into an upper small lobe and a lower large one. In the right lung a second small fissure is directed downwards and back wards from the anterior margin, to end in the great fissure—it cuts off a small triangular piece from the upper lobe, and gives three lobes to the right lung.* From Malpighi to Reisseissen, compre hending the first historical period of Ana tomical Science, the structure of the lungs formed a constant ground of controversy. From Reisseissen (1803) to Rainey, Addison, Rossignol, Schultze, Moleschott, and Adriani, the most recent authors, differences on this subject have continued to divide the opinions of anatornists. This question, which involves so much that is historically interesting in anatomical science, divides itself naturally into two primary departments : 1st, the de scriptive and structural ; and 2nd, the historical bibliography.