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WILLIAM A. LOCY AND OLOP LARSELL 



intercommunicating passages forming bronchial circuits. With 

 this quahfication we may retain the convenient term 'bronchial 

 tree' as applying to the central trunk and its larger branches 

 with their subdivisions, but remembering that the terminal twigs 

 do not end as in the bronchial tree of manmials. The resem- 



Fig. 23 Enlarged view of the lungs of the specimen sketched in figure 22 

 removed from the body. Five air-sacs are shown. The mesial moiet.y of the 

 interclavicular not visible. Modified from a sketch by G. H. A. Rech. 



blance is closer to the capillary connection between arteries and 

 veins than to a tree. 



From their earliest formation, the lung pouches are lined b}' 

 endoderm and this internal cavity is the basis from which hollow 

 buds arise to form branches of the bronchial tree. The endoder- 

 mal tube lies in a layer of mesenchyme that is bordered on the 

 surface towards | the pleuro-peritoneal cavity by a well defined 



