1836 



HUMAN ANATOMY. 



Longitudinal muscle 



Submucous layer 



A layer of connective tissue, representing a siibmucosa, separates the cartilage 

 and muscle from the mucous lining of the trachea. The submucosa contains small 

 aggregations of fat-cells and the tracheal glands. The latter, tubulo-alveolar 

 mucous in type, are most numerous and largest between the rings of cartilage, 

 especially towards the lower end of the trachea. Over the cartilages they are small 

 and often wanting. Their ducts pierce the mucosa to gain the free surface of the 

 latter. 



The mucous membrane^ smooth and attached with considerable firmness to the 

 underlying tissues, is clothed with stratified ciliated columnar epithelium. Many of 

 the surface cells contain mucus and are of the goblet variety. The stroma of the 

 mucosa is rich in fine elastic fibres, which, in the lower part of the trachea, are con- 

 densed into a distinct elastic lamella separating the mucous membrane from the sub- 

 mucosa. Lymphoid cells are constantly found in the mucosa, in places, particularly 

 around the openings of the ducts of the tracheal glands, being aggregated into small 

 collections which suggest lymph-nodules. 



Vessels. — The arteries^ which are insignificant, are branches of the inferior 

 laryngeal from the inferior thyroid, and tend to form a series of horizontal arches 

 between the rings. They anastomose below with the bronchial arteries and with 



the internal mammaries 

 Fig. 1560. through the anterior 



mediastinal twigs. The 

 veinSy arranged like the 

 arteries, belong to the 

 system of the inferior 

 laryngeals. They com- 

 municate with those of 

 the oesophagus, with 

 the thyroid plexus, and, 

 according to Luschka, 

 with the azygos. The 

 lymphatics, which are 

 very numerous, are also 

 disposed in horizontal 

 curves. Leaving the 

 windpipe at the sides 

 of the membranous 

 portion, they open into 

 small tracheal lymph- 

 nodes and communi- 

 cate with the bronchial 

 nodes also. 



The nerves are 

 from the pneumogas- 

 tric and sympathetic 

 nerves. Their ultimate 

 distribution, in addition to the supply for the muscular tissue and the walls of the 

 blood-vessels, includes sensory endings within the mucous membrane which, accord- 

 ing to Ploschko, are similar to those of the larynx. 



The Relations of the Trachea. — The oesophagus, beginning at the lower 

 border of the cricoid cartilage, lies at first behind the trachea, to which it is con- 

 nected by areolar tissue ; but almost at once it is, relatively to the trachea, displaced 

 to the left, to be pushed over again by the arch of the aorta, where this vessel lies 

 on the left of the trachea. The gullet always lies behind the origin of the left bron- 

 chus. Behind the first piece of the sternum the arch of the aorta passes in front of 

 the trachea, which is placed almost symmetrically in the fork made by the innomi- 

 nate and left carotid arteries. The isthmus of the thyroid crosses usually the second 

 and third rings, its lobes resting on the sides of the trachea. The inferior thyroid 

 veins constitute a vascular layer before the lower part of the cervical portion of the 

 trachea. The recurrent laryngeal nerves run up at the back of either side of the 



Epithelium of 

 oesophagus 



— Circular muscle 



Muscle 



Mucous 



fi membrane 



Trachea 



#^ Glands 



Cartilage 



Transverse section of trachea and cesophagus of child, seen from below. X 15. 



