238 ON THE TRACHEA IN THE "RATITE" BIRDS. 



Internally, a very slight thickening of this membrane in an antero- 

 posterior direction, at the bifurcation of the tube, may be seen ; but 

 there is nothing that can be properly called a membrana semilunaris 

 present. The external vocal cord, on the other hand, situated over the 

 first two bronchial semirings, is very well-developed, with a sharply- 

 defined margin. 



On the internal wall of the bronchus there is, in addition, a second, 

 much slighter and less prominent fold, slightly concave forwards, running 

 somewhat obliquely backwards and downwards, and supported by the 

 anterior ends of the third and sixth bronchial semirings. 



Besides Casuarius galeatus, I have examined trachea of CC. beccarii, 

 bennetti, uni-dppendiculatus (2 specimens), and westermani ; and in none of 

 these species can I detect any difference of importance from the arrange- 

 ment I have described above. In the last-named species (an adult specimen) 

 there is a considerable amount of ossification in the last tracheal and 

 first bronchial rings. The mucous fold on the internal walls of the 

 bronchi varies much in development in different specimens. In adults 

 there is a great accumulation of the fibrous and elastic tissues of the 

 mucous membrane in the region of the tracheal tympanum . 



Of Dromceus novce-nollandice I have only, as yet, been able to examine 

 one trachea, and that too from a young specimen. This closely resembles 

 that of Casuarius ; but the number of imperfect tracheal rings seems to 

 be considerably smaller, in the specimen in question only the last three 

 being incomplete behind. The third and fourth bronchial semirings 

 are considerably stronger than the first two and the immediately 

 preceding tracheal rings. There is no pessulus; but the membrana 

 semilunaris, especially posteriorly, seems to be better developed. 



The insertion of the sterno-tracheales is as in Casuarius. The lateral 

 tracheal muscles extend down to within about 1-5 inch of the end of the 

 trachea. 



In the genus Rhea (as represented by R. americana and R. macro- 

 rhyncha) a very different condition of things occurs, there being a highly- 

 specialized and peculiar syrinx, provided with a pair of intrinsic 

 muscles *. 



P. Z. S. 1881, In Rhea americana (figs. 7, 8) the average diameter of the trachea 

 p. 785. 



* I had observed the peculiar syrinx of Rhea some months before I met with M. 

 Alix's short paper on this bird in the " Bulletin " of the Society Philomatique for 1874 

 (p. 38), in which he points out, for the first time, the fact that Rhea possesses a true 

 syrinx. His account, which I here reproduce, runs as follows: "II y a chez le 

 Nandou un larynx inferieur. Les cordes vocales sont placees a 1'origine des bronches, 

 dont les premiers anneaux sont incomplets, en sort que la paroi interne qui leur corre- 

 spond a 1'aspect d'une membrane tympaniforme. Le reste des bronches est forme 

 par des anneaux complete." This description is, as will be seen, very incomplete, and, 

 in the last statement, incorrect. 



