THE RESPIRATORY SYSTEM 



309 



between the ends of the cartilaginous rings are bridged over by a 

 thickened continuation of the fibrous coat, strengthened by a layer 

 of smooth muscle (Fig. 207, m). The bundles of muscle cells run 

 mainly in a transverse direction, and extend across the intervals 

 between adjacent rings as well as between their open ends. There 



X 



" n^}^%- 





/ 





^<Z!^' 



Fig. 207. — Transverse Section of Human Trachea through One of the Cartilage 

 Rings. X8. (KoUiker.) E, Epithelium of {s) mucous membrane; dr, glands; as, 

 gland duct; ad, adenoid tissue; A', cartilage; m, smooth muscle cut longitudinally, 

 extending across between ends of cartilage ring. 



are frequently a few bundles of obHquely disposed cells and, most 

 external, some few that run longitudinally. 



Outside the fibrous coat proper is a looser, more irregular con- 

 nective tissue, which serves to attach the trachea to the surrounding 

 structures. 



Blood-vessels, lymphatics, and nerves have a similar distribution 

 in larynx and trachea. The larger vessels pass directly to the sub- 

 mucosa. From these, smaller l^ranches pass to the different coats, 

 where they break up into capillary networks. 



