60 STRUCTURE AND CLASSIFICATION OF BIRDS 



matter by Foebes.^ There are various grades of this 

 lengthening of the trachea. In certain species of Phony- 

 gama and Manucodia among the Oscines the loops, which 

 vary in complication, lie, as is shown in the figure of 

 Manucodia (fig. 39), beneath the skin. Many of the curassows, 

 a few Scolopacidae {Bhynchcea australis and B. capensis), the 

 duck Anseranas melanoleucd, have a convoluted trachea of 

 the same kind. In the male of Tetrao urogallus the loop is 

 present, but is in the cervical region, not in the thoracic 

 and abdominal, as in the types just referred to. 



The Syrinx. — The voice organ of birds, usually termed 

 the syrinx, is, as is well known, situated at the bifurcation 

 of the two bronchi. Its complexity varies greatly, though 

 it cannot be said that a complex voice organ necessarily 

 implies an elaboration of sound-producing power. Some of 

 the singing birds and the parrots, whose voices are capable 

 of emitting a great variety of tones, have, it is true, a much 

 specialised syrinx. But, on the other hand, there are other 

 passerines which have just as complicated a syrinx, but can, 

 like the raven, by no means vie with some of the starhng 

 tribe, for example, in range of sound. Then, too, some of 

 the singing passerines have syringes which are much simpler 

 than' those of others which sing as well and no better. 

 It is, however, true that in the least differentiated forms of 

 syrinx the bird has but one or two notes. The ostrich, for 

 example, which has one of the simplest syringes, can roar, 

 but possesses no variety of sound. The Apteryx, whose 

 syrinx is about on the same level of organisation, appears 

 to be absolutely mute. The sounds of the emu are due 

 not to its simple syrinx, but, chiefly at any rate, to a 

 throat pouch, to which du^ reference will be made later. 



The syrinx of birds, as has been said, varies considerably 

 in structure. Many of the variations will be treated of in 

 the systematic part of this book, since they are more of 

 systematic than of morphological interest. In this place, 

 however, the leading modifications of the organ will be 



' ' On the Convoluted Trachea of two Species of Manucode, with Remarks on 

 similar Stractures in other Birds,' P. Z. S. 1882, p. 347. 



