64 



STRUCTURE AND CLASSIFICATION OF BIRDS 



side it is convex upwards, as are its immediate predecessors 

 in a less degree. The interannular intervals between all 

 these rings are, when undisturbed, mere chinks filled up 



FIG. 43. SYRINX OF titridhio. 



a, last, <M, penultimate, ooo antepenultimate tracheal rings : I, section of wall of wind- 

 pipe to show vocal chord ; 1-7, tracheal, I, II, bronchial rings. (After FOHUKS. ) 



by dense fibrous and elastic tissue. There is no trace of a 

 pessulus, though the last tracheal ring is slightly produced 



FIG. 44. THE SAME SYRINX FROM BEHIND. 



downwards in front. The first bronchial semi-ring on each 

 side is narrow and cylindrical, strongest anteriorly, and 

 somewhat attenuated posteriorly. It is separated only by a 



