1840 HUMAN ANATOMY. 



The dimensions of the lung-roots are difficult to determine. They are nar- 

 rower below than above and shorter behind than in front. The lower posterior bor- 

 ders, which are formed by the inferior pulmonary veins, are of about the same length 

 (2 cm. ) on each side and very symmetrical. We may put the right root in front and 

 above at from 4-4.5 cm. and the left at about i cm. longer. They are thickest 

 above, and expand as they approach the hilum of the lung, where the diameter is 

 approximately 3.5 cm., the left one being rather the thicker. The height at the 

 hilum is from 5-6 cm., probably sometimes rather more. 



The Relations of the Roots. — Below lies the pericardium covering the heart, 

 chiefly the left auricle. The great azygos vein arches over the right root from be- 

 hind, to join the superior vena cava, which is against the root in front. The arch of 

 the aorta crosses the left root from before backward, being less closely applied to it 

 behind than elsewhere. The oesophagus is behind the very beginning of the left 

 root. The pleura is reflected over each root, which it completely envelops as it 

 passes from the parietal into the visceral layer. The broad ligament of the lungs is a 

 fold of pleura extending downward from the end of the root. The phrenic nerve 

 of each side passes in front of the root, between the pericardium and the pleura. 



PRACTICAL CONSIDERATIONS : THE AIR-PASSAGES. 



The Trachea and Bronchi. — The elasticity and mobility of the trachea, the 

 compressible character of its walls, the loose cellular tissue in which it lies, and the 

 variety of the structures with which it is in close relation should all be remembered 

 in considering its injuries and diseases. 



Wounds of the cervical portion of the trachea — as in cut throat below the cricoid 

 — are not rare. The trachea is rendered more superficial by extreme extension of 

 the neck, and is also elongated. A deep wound may therefore sever it completely, 

 in which case the lower end may retract below the level of the superficial wound, 

 making the hurried introduction of a tracheotomy tube difficult. 



Rupture — "fracture" — of the cervical trachea has resulted from contusion, and 

 in the presence of pre-existing disease has followed coughing. The depth of the 

 thoracic trachea protects it from all but penetrating wounds, and these, on account 

 of the important structures also implicated, are usually fatal. 



Disease beginning in or confined to the trachea is rare, but it may be involved 

 in the extension of either bronchial or laryngeal morbid processes. The normal 

 tracheal mucous membrane is said to resist cadaveric disintegration longer than any 

 other mucous membrane of the body (Elsberg). 



Stenosis of the trachea, if from intrinsic change, is usually due to ulceration, 

 either syphilitic or tuberculous, followed by cicatrization. It is, however, far more 

 commonly due to extrinsic causes, the mechanism of which will be readily under- 

 stood if the relations of the trachea are recalled (page 1836). From above down- 

 ward it is evident that the trachea may be compressed by enlargements of the thyroid 

 gland, by retro-oesophageal tumors or abscesses, by carotid, innominate, or aortic 

 aneurism, or by lymphatic swellings in the neck or near the bifurcation. As the 

 posterior part of the tracheal wall is musculo-membranous (partly in order to avoid 

 undue pressure of the trachea on the oesophagus), the impaction of a foreign body in 

 the latter tube may cause tracheal narrowing. The trachea may be involved in dis- 

 ease originating elsewhere, as in tuberculous infection of the thoracic lymphatic 

 glands, or in carcinoma of the same glands, or of the cervical chain, or of the oesoph- 

 agus. Abscesses or aneurisms may ulcerate through its walls and empty into its 

 lumen, suffocating the patient. The close relation of the trachea to the aorta makes 

 it possible in some cases of aortic aneurism to hear a systolic bruit either in the 

 trachea or at the patient's mouth when opened. This is either the sound conveyed 

 from the sac or is produced by the air as it is driven out of the trachea during the 

 systole (Osier). The sign known as "tracheal tugging" also depends upon the 

 same close relation. With the patient erect, his mouth closed and his chin elevated, 

 when the cricoid is grasped between the finger and thumb and pressed gently and 

 steadily upward, if aortic aneurism or dilatation exists, the pulsation of the aorta 

 will be distincdy transmitted through the trachea to the hand (Oliver). 



