12 6 MORPHOLOGICAL TYPES 



trachea from the angle between the bronchi, forming the 



p IG 58.— Columba : ventral view of a dissection to show the air-sacs. 

 a, abdominal air-sac ; at, anterior thoracic air-sac ; c, cervical air-sacs ; 

 co, coracoid ; die, diverticulum of the interclavicular air-sac ; /, iurcula ; 

 ^/humerus (which contains a diverticulum from ic) ; i, intestine ; ic, inter- 

 clavicular air-sac ; pt, posterior thoracic air-sac ; r, rib ; s, sternum ; tr, 

 trachea. 



syrinx, by the vibrations of which birds sing. The bronchi 



