THE LUNGS. 



165 



Fig. 234. 



chondrium and, especially, in the mucous membrane, in which 

 they are disposed as in the pharynx (vide p. 393) j the branches 

 going to the epiglottis are also furnished with microscopic 

 ganglia. 



[The glands of the larynx and of the air-passages are fre- 

 quently altered in catarrh, so that their vesicles measure as 

 much as 0-08'", or even 0-15'", and are filled with minute, 

 rounded cells, which may probably be compared with the 

 mucous corpuscles formed on the surfaces of mucous mem- 

 branes.] 



§ 174. 

 The trachea and its branches are united to the contiguous 

 parts by a connective tissue abound- 

 ing in well-defined elastic fibres ; they 

 are then surrounded by a tough, elas- 

 tic, fibrous tissue, which covers the car- 

 tilaginous rings, like a perichondrium, 

 connects them together, and, in a some- 

 what thinner layer, invests the pos- 

 terior membranous wall of the canal 

 in question. To this layer succeed 

 the cartilages, in front and on the 

 sides, while posteriorly there is a layer 

 of smooth muscles. The former, ± — J'" 

 thick, are constituted exactly like the 

 larger cartilages of the larynx, but ex- 

 hibit no tendency to become ossified. 

 The muscles, on the contrary, from 

 the trachea onwards, cease to be of 

 the striped kind and constitute, on the 

 posterior wall of the tube, only an 



Fig. 234. Vertical section through the anterior 

 wall of the human trachea, x 45 diam. : a, fihrous 

 coat ; b, c, d, cartilage ; b, external layer, with flat- 

 tened cells ; d,internal layer,with elongated elements; 

 e, submucous connective tissue ; /, portion of a 

 mucous gland ; g, elastic longitudinal fibrous layer ; 

 h, epithelium, on which the cilia are not visible ; i, 

 glandular orifice. 



SBJftVS* 



