DEVELOPMENT OF LUNGS AND BUOYANCY STRUCTURES 



647 



ESOBRONCHUS 



RECURRENT BRONCHI 



ABDOMINAL AIR SA 



NTERMEOIATE 



Fig. 308. Respiratory structures in adult birds. (A after Kingsley, '12, Comparative 

 Anatomy of Vertebrates, Philadelphia, P. Blakiston's Son & Co.; B slightly modified from 

 Goodrich, '30.) (A) Syrinx or voice box of canvasback, Aythya. (B) Diagram of 

 left side view of lungs and air sacs of an adult bird. 



bronchus, an outgrowth of the mesobronchus at the anterior extremity of the 

 lung. The anterior intermediate, posterior intermediate, and the interclavicular 

 air sacs take their origins from the ventral surface of the lungs and represent 

 outgrowths from the entobronchi (figs. 306G, 307A). The interclavicular air 

 sac arises from the fusion of four moieties, two from each lung. The air sacs 

 lie among the viscera and send out slender diverticula, some of which may 

 enter certain bones (fig. 308B). 



3) Formation of the Bronchi and Respiratory Areas of the Chick's Lung. 

 Internally, the primary bronchial division of each lung passes into the lung's 

 substance where it continues as the mesobronchus. The mesobronchus thus 

 represents a continuation of the main or primary bronchial stem of the lung 

 and is a part of the original entodermal outpushing from the pharynx. From 

 the mesobronchus, the ectobronchi and entobronchi arise as diverticula (fig. 

 307A, B). The parabronchi or lung pipes develop as connections between the 

 ectobronchi and entobronchi (fig. 307B). The parabronchi constitute the 

 respiratory areas of the lung, for the parabronchi send off from their walls 

 elongated diverticula, the infundibula or vestibules. The vestibules are 

 branched distally (fig. ,307C) and anastomose with each other to form the 

 air capillaries. The blood capillaries (fig. 307C) ramify profusely between the 

 air capillaries. It is not clear that the air capillaries possess definite cellular 

 walls throughout. 



As indicated in figure 307D, other or recurrent bronchi are formed as air 

 passages which arise from the air sacs and grow back into the lungs, where 

 they establish secondary connections with the other bronchi. The air sacs thus 

 represent expanded parts of the bronchial circuits of the kings which not only 



