A XVI I.] 



THE RESPIRATORY ORGANS. 



297 



layers -some are pear-shaped and the lowest more oval. Very 

 frequently a thin layer of mucus is adherent to the cilia. The 

 arrangement of the cells of the mucous layer is the same as in the 

 bronchus (fig. 286). 



2. L.S. Trachea (fig. 284) (L and H). Compare these with the 

 previous section. The coats are the same, but several oval pieces 

 of hyaline cartilage are seen one after the other embedded in the 

 fibrous coat. The elastic fibres are now seen arranged longitudi- 

 nally. The acini of the mucous glands are most numerous in the 

 interspaces between the cartilages, and amongst the acini may be 

 seen leucocytes and some adenoid tissue. If a gland-duct be found, 

 it opens by a funnel-shaped expansion on the free surface of the 

 mucous membrane. If it be desired to study the glands, use 

 hcematoxylin and eosin as stains. 



3. T.S. Human Trachea (L and H). Observe the general 

 similarity to the previous prepara- 

 tion. Here, however, the glands 



are well-developed ; the basement 

 membrane is well marked, and in 

 picro-oarmine specimens is stained 

 red. Some of the superficial epi- 

 thelial cells are apt to be detached. 



4. T.S. Intra-Pulmonary Bron- 

 chus. (a.) (L) Observe the fibrous 

 coat, and outside it the vesicular 

 tissue of the lung. In the fibrous 

 coat two or three pieces of 

 hyaline cartilage. The submucous 

 coat, with its glands (fig. 285). 



(b.) Inside this a complete ring 

 of smooth muscle bronchial muscle 

 perforated here and there by the 

 ducts Of .the glands. Immediately Fw 

 inside this, in the mucous coat, 

 several layers of longitudinal elastic 

 fibres cut transversely. Most in- 

 ternal, ciliated epithelium, like 

 that lining the trachea, and resting 



on a basement membrane. The mucous membrane is frequently 

 thrown into ridges or folds. 



(c.) In the fibrous coat, external to the cartilages, search for 

 sections of two large vessels the pulmonary artery and vein and 

 of small branches the bronchial vessels. Also several sections of 

 nerves; in the course of some of them may be found ganglionic 

 cells. 



27 



Membrane of 

 Human Bronchus, a. Mucus ; b. 

 Ciliated cells ; c. Deep cells; d. Base- 

 ment membrane ; e. Longitudinal 

 elastic fibres ; /. Bronchial muscle ; 

 g. Connective tissue, with leucocytes 

 and pigment. 



