THE EMBRYOLOGY OF THE BIRD'S LUNG 



BASED ON OBSERVATIONS OF THE DOMESTIC FOWL 

 WILLIAM A. LOCV AND OLOF LARSELL 



TWENTY-TWO FIGURES 



PART III 



3. THE AIR-SACS AND THE RECURRENT BRONCHI 



Morphologically considered, the air-sacs and recurrent bron- 

 chi are parts of the bronchial tree, but on account of their impor- 

 tance in the avian lung and their unusual interest they are sepa- 

 rately considered in this section. This plan also promotes 

 clearness of description, since, at best, the bronchial tree is very 

 complex. The recurrent bronchi, in particular, should receive 

 special notice, because they have been recently recognized and are 

 of capital importance in the physiological anatomy of the lungs. 



The name 'recurrent bronchi' has been given to certain bron- 

 chial tubes that grow from the air-sacs into the lungs of birds to 

 connect with the other air passages. In this sense they are 

 'recurrent.' They are outgrowths from the air-sacs, rather than 

 extensions of the bronchial tree from within the lung, and the 

 air-sacs and recurrent bronchi are so intimately related in their 

 development that the two structures should be considered to- 

 gether. In the course of development they unite with twigs of 

 the bronchial tree and thus establish complete circuits with the 

 air passages within the lungs. In the adult lung the air passes 

 from the air-sacs through these recurrent bronchi, entering the 

 lung by a returning current, and, in this sense, the air circuit 

 through these bronchi is a recurrent one. 



The credit for the recognition of the morphological arrange- 

 ment as well as for the part which recurrent bronchi play in the 

 respiration of birds should be divided between Schulze ('09 and 



1 Part I of this ])aper appeared in the American Journal of Anatomy, vol. 19, 

 no. 3, May, 1916. 



1 



THE AMEKIC.VN JOURNAL OF AJ« ATOMY, VOL. 20, NO. 1 

 JUL\-, 1916 



