THE RESPIRATORY ORGANS. 



169 



b. The submucous coat is of areolar fibrous tissue, supporting the 

 mucous glands that open into the trachea, and the bloodvessels, 

 lymphatics, and nerves, and also little masses of adipose tissue. In 

 the neighborhood of the cartilages this fibrous tissue becomes con- 

 densed to form the perichondrium. 



c. The cartilages are composed of the hyaline variety of that 



FIG. 145. 



From a longitudinal section through the trachea of a child. (Klein.) a, the stratified 

 columnar ciliated epithelium of the internal free surface ; b, the basement -membrane ; 



c, the mucosa (tunica propria) ; d, the network of longitudinal elastic fibres (the oval nuclei 

 between them indicate connective-tissue corpuscles) ; e, the submucous tissue, con- 

 taining mucous glands; /, large bloodvessels; g, fat-cells: h, hyaline cartilage of the 

 tracheal rings. (Only a part of the tracheal wall is given in the figure.) 



tissue, and are incomplete rings, interrupted behind, where the two 

 ends are united by a band of smooth muscular tissue. 



d. The fibrous coat is of areolar tissue beyond the bounds of the 

 perichondrium, and serves to connect the trachea with its sur- 

 roundings. 



3. The Bronchi. The main bronchi branching from the trachea 

 have a structure similar to that organ, but the cartilaginous rings 

 become more delicate as the tubes diminish in size. 



