THE TKACHEA AND LUNGS 121 



The lympboid tissue is especially abundant in the mucous mem- 

 brane of the ventricle of Morgagni, and a large number of mucous 

 glands open into this cavity and into that of the sacculus. 



The true vocal cords are composed of fine elastic fibres. 



The cartilages of the trachea and larynx are hyaline, except the 

 epiglottis and the cartilages of Santorim and of Wrisberg, which are 

 composed of elastic fibro-cartilage. 



FIG. 145. DIAGRAMMATIC REPRESENTATION OF THE ENDING OF A 

 BRONCHIAL TUBE IN SACCULATED INFUNDIBULA. 



The lungs are formed by the ramifications of the bronchial tubes 

 and their terminal expansions, which form groups of sacculated dila- 

 tations (infundibula), beset everywhere with small hemispherical 

 bulgings, known as the air-cells on pulmonary alveoli. 



deb 



FIG. 146. PORTION OF A TRANSVERSE SECTION OF A BRONCHIAL TUBE, HUMAN 

 6 MM. IN DIAMETER. (Magnified 30 diameters.) 



a, cartilage and fibrous layer with mucous glands, and, in the outer part, a little fat ; in the 

 middle, the duct of a gland opens on the inner surface of the tube ; 6, annular layer of 

 involuntary muscular fibres ; c, elastic layer, the elastic fibres in. bundles which are seen 

 cut across ; d, columnar ciliated epithelium. 



The bronchial tubes (figs. 146, 147) are lined in their whole 

 extent by ciliated epithelium which rests on a basement-membrane. 

 External to this is the corium of the mucous membrane, containing a 

 large number of longitudinal elastic fibres and some lymphoid tissue. 



