306 A. 0. V. Ti/iKiiifi: Syrinx of Fowl. 



Oe Oesophagus. 



p Pessulus. 



pi Pleural cavity. 



sa Anterior thoracic air sac. 



sai Common stem of tlie anterior thoracic and interclavicular 



sacs, 



sb, sW Right and left iuterbronchial sacs, 



sc Cervical air sac. 



sdU, sdl2 Dorso-lateral sacs. 



si Interclavicular air sac. 



sp. Subpessular sac. 



sr, sri Large and small recurrent interclavicular branches, 



svli. svl2 Ventro-lateral sacs. 



T " Tympanum," or syringeal chamber. 



ti-t^ Lower six tracheal cartilaginous rings; t^-t^, fused. 



Th Trachea. 



V Ventral triangular plate. 



