THE TRACHEA AND BRONCHI 



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homogeneous basement membrane. This is penetrated here and there by- 

 channels which connect the adenoid tissue of the mucosa with the inter- 

 cellular substance of the epithelium. The stratified columnar epithelium 

 is formed of several layers, of which the most superficial layer is ciliated and 



FIG. 220. Ciliary Epithelium of the Human Trachea, a, Layer of longitudinally 

 arranged elastic fibers; &, basement membrane; c, deepest cells, circular in form; d, inter- 

 mediate elongated cells; e, outermost layer of cells fully developed and bearing cilia. X 

 350. (Kolliker.) 



the cells often branched downward. Many of the superficial cells are of the 

 goblet variety. In the deeper part of the mucosa are many elastic fibers 

 between which lie connective-tissue corpuscles and capillary blood vessels. 



Numerous mucous glands are situated on the exterior and in the substance 

 of the fibrous framework of the trachea, their ducts perforating the various 



FIG. 221. Transverse Section of a Bronchus, about $ inch in Diameter, e, Epithelium 

 (ciliated); immediately beneath it is the mucous membrane or internal fibrous layer, of 

 varying thickness; m, muscular layer; s, m, submucous tissue;/, fibrous tissue; c, cartilage 

 enclosed within the layers of fibrous tissue; g, mucous gland. (F. E. Schulze.) 



structures which form the wall of the trachea, and opening through the 

 mucous membrane into the cavity of the trachea. 



The two bronchi into which the trachea divides resemble the trachea 

 in structure, with the difference that in them there is a distinct layer of un- 

 striped muscle arranged circularly beneath the mucous membrane, forming 



