THE EMBRYOLOGY OF THE BDID S LUNG 



21 



minal portions of secondary branches of the bronchial tree. 

 Thus the recurrent bronchi sustain the same relation to the air- 

 sacs that the parabronchi do to the respective secondary branches 

 from which they have their origin. 



2. By means of the recurrent bronchi and their anastomoses 

 with other branches of the bronchial circuits the air-sacs are 

 brought into communication with all parts of the lung. They 



O.Lat 



Rec.Or. -- 



Rec.Or. 



A.lnt.Sc." 



Tr.B 



O.P.Int.Sc 

 Rec.Or. 



O.Cerv.Sc. 



Fig. 54 Diagram of the ventral aspect of the adult lung constructed from 

 studies of the prepared lung and from Wood's metal casts. Shows the nature of 

 the seven orifices into the air-sacs as described in the text. DO., direct orifices, 

 Rf'c.O.. orifices of recurrent bronchi. 



have direct communication with bronchus and central lung tube 

 through their 'direct orifices' and a recurrent communication 

 through the recurrent bronchi. 



3. The unpaired interclavicular air-sac of the adult fowl is the 

 result of fusion of four embryonic outgrowths : two moieties from 

 each lung which first unite and then undergo fusion across the 

 median line to form the single interclavicular air-sac. 



