258 



RESPIRATION, ORGANS OF. 



RESPIRATION. ORGANS OF. I. Hu- 

 man and Mammalian. f\ie respiratory system 

 of organs in man and mammalia comprehends - 

 the larynx, the trachea, and the lungs : embry- 

 ologically, the thyroid and thymus glands 

 should be included in this category. The em- 

 bryonic apparatus of the branchial arches falls 

 under the same denomination. In this article 

 the trachea, bronchi and lungs only will be 

 studied, in their general and minute anatomy. 

 These parts in the human subject will be 

 described at length. In mammalia the pro- 

 minent varieties of structure occurring in some 

 of the commoner genera will be incidentally 

 noticed. 



THE LUNGS (wev/tai>, Gr. ; Pufmo, Lat. ; 

 Poumon,T?\\;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 time. 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 from 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 puhnonalis 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 vertebras. 



It is longer than the anterior. The posterior 

 and inferior margins descend into the 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 anatomists. 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. 



The Trachea in man extends from the 

 larynxf to the bifurcation of the tube into the 

 right and left bronchi ; its first superior ring, 

 which is attached to the cricoid cartilage, 

 coincides with the upper border of the body 

 of the fifth cervical vertebra : the point of its 

 bifurcation in the thorax is level with the 

 superior edge of the body of the third dorsal 

 vertebra : it averages in internal diameter 

 from f of an inch to 1 inch, and in length 

 from 4 inches to 4i inches. J Variations in 

 the length of the trachea are due to the great 



* For a full account of tbe relations of the lungs 

 to the thorax and to the neighbouring viscera, see 

 art. THORAX. 



f See Art. LAHYNX. 



j " Trachea, 3" 4i" longa, 8'" 12"' ]ata, et 

 e pariete anteriore ad posterior em, 7'" 9'" anipla 

 est." Disquisitiones de Structura et TexturaCana- 

 lium acriferum. Scripsit Eruestus Schultze. Mi- 

 tavire et Lipsiic, 1850. 



