KESPIRATORY ORGANS 



409 



strengthened with bony rings, leads back along the neck, lying 

 at first below the gullet and then at its left side. At the base of 

 the neck it divides into the two bronchi ; the hinder end of the 



cer. 5 



p.tk.s. 



a. tk.s. 



Fig. 3 2 3.-^ a diagram of a lung and its air sacs in the pigeon. 



ab.s., Abdominal sac ; a.th.s., anterior thoracic sac ; br., bronchus ; cer.s., cervical sac ; icl.s., interclavicular 

 sac ; L, lung ; p.th.s., posterior thoracic sac ; r.br., recurrent bronchi ; tra., trachea. The arrows show 

 the direction of the air currents. 



s.cerv 



S. thor 

 ant 



s. cLav. 



ax. 



s tnonpozt 



s cbd 



Fig. 324.— Diagram of the lungs and air sacs of the pigeon. On the left : the ventral 

 surface of the lungs, the expiratory bronchi, and air sacs. On the right : the 

 inspiratory bronchi and air sacs in black. — From Young, The Life of 

 Vertebrates, 1950. Clarendon Press, Oxford. After Brandes and Ihle. 



B., Main bronchus; C, cervical ventro-bronchus ; .1/., mesobronchus ; V., vestibule; s.abd., abdominal 

 air sac ; s.cerv., cervical air sac ; s.clav., clavicular air sac with diverticulum (ax.) in axilla ; s.thor.ant., 

 anterior and sJhor.post., posterior, thoracic air sac. 



M.Z. — 14 



