OCR Text |
Show 1881.] TRACHEA IN THE " RATITE " BIRDS. 787 in the structure of its syrinx. In the single specimen I have by me, the tympanic box is anteriorly marked by four sutures on one side, and by three only on the other, as sometimes happens in B. americana (as, e. g., 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 Bhea 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 Bhea stands out by itself as sharply opposed to all the remaining "Ratite" birds. Of the latter, Struthio and Apteryx, as far as regards tracheal structure, form one group, the Casuariidae another, the difference between the two being, however, comparatively slight as compared with those between them generally and Bhea. 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 be-between the two constituent 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 stemo-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 Bhea. 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 a pessulus ; 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 Ratite birds have no voice-organs1. As I have here shown, all these three structures are 1 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 the Gallinse, Ducks, Chauna, and many other noisy birds should be voiceless. As regards the Batitse, the statement made by Meckel that they are mute or nearly so (I.e. p. 571), is, I believe, equally groundless. I a m assured by M r. Bartlett that all, except perhaps the Apteryx, have the power of making considerable noises. As regards the Ostrich, indeed, Livingstone states that it is frequently difficult to distinguish its bellowing from the roaring of the Lion, |