308 



THE ORGANS 



epithelium, with numerous goblet cells, resting upon a broad base- 

 ment membrane, and of a stroma of mixed fibrous and elastic tissue 

 containing many lymphoid cells. 



The submucosa is not distinctly marked off from the stroma on 

 account of the absence of a muscularis mucosae. It is distinguished 

 from the stroma by its looser, less cellular structure, by its numerous 

 large blood-vessels, and by the presence of glands. These are of the 

 simple branched tubular variety and are lined with both serous and 



'■^^■'.J\ '."•«■ 





■Si^ 



Fig. 2o6. — From Longitudinal Section of Human Trachea. X40. (Technic 3, p 

 310.) a, Epithelium; 6, stroma; c, cartilage; d, fibrous coat; c, serous tubules;/, mucous 

 tubules; g, glands in submucosa; h, ducts. 



mucous cells. Some of the mucous tubules have well-marked cres- 

 cents of Gianuzzi. The glands are most numerous between the ends 

 of the cartilaginous rings, where they frequently penetrate the muscle 

 and extend into the fibrosa. 



The fibrosa is composed of coarse, rather loosely woven connect- 

 ive-tissue fibres embedded in which are the tracheal cartilages. These 

 are incomplete rings of hyahne cartilage shaped like the letter C 

 (Fig. 207). They are from sixteen to twenty in number and encircle 

 about four-fifths of the tube, being open posteriorly. The openings 



