64 



STEUCTURE 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 



Pig. 43. — ^Syrijjx or Struthio. 



0, last, 00, penultimate, ooo antepenultimate tracheal rings ; &, section of wall of wind- 

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



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 Sybinx ibom 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 



