50 THE STORY OF THE BIRDS 



in what are known as the Oscines or Singing 

 Passeres. Most of these birds possess five or 

 seven pairs of syringeal muscles. The four or 

 five distal tracheal rings are fused solidly together 

 into a little box or chamber communicating with 

 the bronchial tubes, the first and second bronchial 

 semi-rings being closely attached to the trachea ; 

 and the spaces between the second and third, 

 and third and fourth semi-rings, being gene- 

 rally closed by outer tympaniform or drumlike 

 membranes, whilst the remaining semi -rings 

 are closed by an inner similar membrane. The 

 result of the manipulation of these muscles in 

 endless combinations of rotating and rocking 

 movements is the utterance through this tracheal 

 sounding pipe of those lovely songs for which 

 the true singing birds are so justly famed. Three 

 types of Syrinx are recognised by anatomists, 

 dependent upon the position of the sound- 

 producing membranes, and termed Tracheal, 

 Bronchia, and Tracheo-Bronchial respectively. 

 The first-named type includes birds that possess 

 a loud voice, and form the well-marked group of 

 Clamatore Passeres, confined to the Neotropical 

 Region. In the second type the trachea has no 

 sounding membranes, and includes various Goat- 

 suckers and Swifts, whilst there are certain forms 



