ON THE TRACHEA IN THE " RATITE " BIRDS. 241 



Rliea macrorliynclia closely resembles, in all respects, R. americana in 

 the structure of its syrinx. In the single specimen I have by me, the P ' Z> ,?- J 881 

 tympanic box is anteriorly marked by four sutures on one side, and by 

 three only on the other, as sometimes happens in R. americana (as, e. </., 

 in the specimen described and figured above). 



Reviewing the facts herein detailed, the most striking fact that comes 

 out is the great difference exhibited by Shea when compared with the 

 four other genera described. In the possession of a tracheal box formed 

 by the fusion of the few last tracheal rings, in the greater amount of 

 specialization of the first two bronchial semirings of each side, in the 

 presence of distinct interannular membrane-covered fenestrae, in the 

 development of a well-marked cartilaginous pessulus, and in the possession 

 of a pair of true intrinsic syringeal muscles running from the trachea to 

 the bronchial semirings Rhea stands out by itself as sharply opposed to 

 all the remaining " Ratite " birds. Of the latter, Struihio and Apteryx, 

 as far as regards tracheal structure, form one group, the Casuariid 

 another, the difference between the two being, however, comparatively 

 slight as compared with those between them generally and Rhea. 



Struthio and Apteryx, in the tendency of the trachea to narrow before 

 its bifurcation, in the greater amount of solidity of the cartilaginous 

 structures, in the more sharply-defined junction between the two con- 

 stituent parts of the bifurcating trachea, owing to the better development 

 of the few last tracheal rings, differ from the Casuariidae, where the 

 terminal part of the trachea tends to develop into an expanded tympanum, 

 the cartilaginous structures are softer and more pliant, the terminal 

 tracheal rings are narrower, and tend, especially in Casuarius, to become 

 imperfect posteriorly, and the junction of trachea and bronchi is less 

 marked. In the Casuariidae, too, the insertion of the sterno-tracheales is 

 different from that of the other genera. 



As regards the alleged absence of a lower larynx (or " syrinx ") in 

 these " Ratite " birds, it is obviously untrue as regards the genus Rhea. 

 In the other genera, an answer is less easy, and its nature must depend 

 upon what is meant by the term " lower larynx." 



The presence of intrinsic voice-muscles cannot be regarded as essential 

 in the definition of that term, any more than the development of apes- 

 sulus ; indeed either or both (e. g. Conopophaga) may be absent in birds 

 with well- developed vocal organs. If the presence of semirings externally, 

 and of a membrana tympaniformis internally, forming the walls of the 

 bronchi, and of vocal cords developed in the interior of those tubes, be 

 held to be sufficient to characterize a " syrinx," then it will be incorrect 

 to say that the Eatite birds have no voice-organs *. As I have here shown, 



* It is sometimes, though most erroneously, supposed that because a bird has no 

 intrinsic voice-muscles, it is, therefore, mute. Were such the case, all (he Gallinje, 



B 



