i6o 



STRUCTURE OF THE TRACHEA. 



cells under them. [The superficial layer of cells is columnar and ciliated (fig. 130, b), while 

 those lying under them present a variety of forms, and below all is a layer of somewhat flat- 

 tened squames, c, resting on the basement membrane, d. These squames constitute a layer 

 quite distinct from the basement membrane, and they form the layer described as Debove's- 

 membrane. They are active germinating cells, and play a most important part in connection 



with the regeneration of the epithelium, 

 after the superficial layers have been 

 shed, in such conditions as bronchitis. 

 Not unfrequently a little viscid mucus 

 (a) lies on the free ends of the cilia. In 

 the intermediate layer, the cells are more 

 or less pyriform or battledore-shaped, 

 with their long tapering process inserted 

 amongst the deepest layer of squames. 

 According to Drasch, this long process is 

 attached to one of these cells and is an 

 outgrowth from it, the whole constituting 

 a "foot-cell."] 



Under the epithelium is the homo- 

 geneous basement membrane, through 

 which fine canals pass, connecting the 

 cement of the epithelium with spaces in 

 the mucosa. [This membrane is well 

 marked in the human trachea, where it 

 plays an important part in many patho- 

 logical conditions, e.g., bronchitis. It 

 is stained bright red with picrocarmine.] 

 The cilia act so as to carry any secretion 

 towards the larynx. Goblet cells exist 

 between the ciliated columnar cells. 

 Numerous small compound tubular 

 mucous glands occur in the mucous 

 membrane, chiefly between the cartilages. 

 Their ducts open on the surface by means 

 of a slightly funnel-shaped aperture, into 

 " the " 



which the ciliated epithelium is prolonged 

 for a short distance. [The acini of some 

 of these glands lie outside the trachealis 

 muscle. The acini are lined by cubical 

 m r ^'r i i , , v or columnar secretory epithelium. In 



lransverse section of part of a human bronchus ( x 450). some animals (dog) these cells are clear, 

 a, precipitated mucus.; b, ciliated columnar epithe- an( i pre sent the usual characters of a 

 hum ; c, deep germinal layer of cells (Debove's mem- muC us-secreting gland ; in man, some of 

 brane); rf elastic basement membrane; e y elastic the cells may be clear, and others "gran- 

 fibres divided transversely (inner fibrous layer); /, u ] arj but t h e appearance of the cells 

 bronchial muscle ; g, outer fibrous layer with leuco- depends upon the physiological state 

 cytes and pigment granules (black); below a mass of activity.] These glands secrete the 

 of adenoid tissue. mucus, which entangles particles inspired 



with the air, and is carried towards the larynx by ciliary action. [Numerous lymphatics exist 

 in the mucous and sub-mucous coat, and not unfrequently small aggregations of adenoid tissue 

 occur (especially in the cat) in the mucous coat, usually around the ducts of the glands. They 

 are comparable to the solitary follicles of the alimentary tract. The blood-vessels are not so 

 numerous as in some other mucous membranes. [A plexus of nerves containing numerous 

 ganglionic cells at the nodes exists on the posterior surface of the trachealis muscle. The 

 fibres are derived from the vagus, recurrent laryngeal, and sympathetic {C. Frankenhatiser, W. 

 Stirling, Kandarazi).] 



[The mucous membrane of the trachea and extra-pulmonary bronchi, therefore, consists of 

 the following layers from within outwards : 



(1) Stratified columnar ciliated epithelium. 



(2) A layer of flattened cells (Debove's membrane). 



(3) A clear homogeneous basement membrane. 



(4) A basis of areolar tissue, with adenoid tissue and blood-vessels, and outside this a layer 



of longitudinal elastic fibres. 



Outside this, again, is the sub-mucous coat, consisting of loose areolar tissue, with the larger 

 vessels, lymphatics, nerves, and mucous glands.] 

 [The Bronchi. In structure the extra-pulmonary bronchi resemble the trachea. As they 



