1 128 



A MANUAL OF ANATOMY 



ring is deep, and its lower border projects backwards so as to form a ridge 

 between the openings of the two bronchi. 



In the posterior wall of the trachea, within the fibrous layer, there is a con- 

 tinuous layer of unstrlped muscular tissue, the fibres of which extend trans- 

 versely between the ends of the rings to which they are attached. In the 

 intervals between the extremities of the rings they are attached to the fibrous 

 coat. These fibres serve to approximate the ends of the rings, and so diminish 

 the calibre of the tube. 



The submucous coat consists of loosely-arranged areolar tissue, and contains 

 the larger bloodvessels and nerves, together with the mucous glands. 



The mucous coat consists of areolar and elastic tissues, and a large amount 

 of lymphoid or adenoid tissue. It contains the ramifications of the arteries 

 and nerves, as well as the lymphatics. Superficial to the mucosa there is a 



well-marked base- 



ment membrane 

 ^k^ntCbra^ which Supports the 

 Mucosa epithehum. The 



deep portion of the 

 mucosa consists 

 principally of elas- 

 tic fibres. On the 

 posterior wall these 

 elastic fibres are 

 very nuiHerous, 

 and are arranged 

 in longitudinal 

 bundles which give 

 rise to elevations 

 of the mucosa. 



The epithelium is 

 of the stratified 

 columnar ciliated 

 variety. 



The wall of the 

 trachea contains 

 many mucouS 

 glands. Some of 

 these are situated 

 in the submucous 



Ciliated Epithelium 



Elastic Fibres 



Submucosa, with 

 Mucous Glands 



Hyaline Cartilage 

 of Ring 



Fibrous Investment 



Fig. 461A. — Longitudinal Section of the Trachea. 



coat. Others, which are of large size, are situated on the posterior wall, 

 where they are very superficial, many of them, Uke small grains, lying super- 

 ficial to the fibrous layer, where they are quite visible. Others are contained 

 within the fibrous layer. The ducts of these glands have to pass through 

 (i) the muscular layer, (2) the elastic layer (part of the mucosa), and (3) the 

 mucosa, upon the surface of which they open by apparent orifices. 



Development. — The trachea is developed from the lower part of a median 

 diverticulum from the ventral aspect of the fore-gut superiorly, the upper part 

 of this diverticulum giving rise to the larynx. 



OSsophagus. — The oesophagus is that part of the alimentary canal 

 which extends from the pharynx to the stomach. In the neck it 

 commences on a level with the lower border of the cricoid cartilage, 

 and terminates on a level with the upper border of the manubrium 

 sterni. It is compressed from before backwards, and lies between 

 the trachea and the vertebral column covered by the longus colli 

 muscles. At first it occupies the median line, but as it descends 

 it inclines slightly to the left side, so as to be partially visible on the 

 left side of the trachea. 



Relations — Anterior. — The trachea; the posterior parts of the 

 lateral lobes of the thyroid body; the recurrent laryngeal nerves; 



