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Show 1886.] TRACHEA AND SYRINX IN CERTAIN BIRDS. 323 In the Ardeidse, on the other hand (including the Herons, Bitterns, arid Scopus, which to this extent is a Heron1), the syrinx has what may perhaps be called a more typical form. The bronchi are short, and the rings which compose them are only half-rings, and are completed on the inner side by membrane; there is a pair of intrinsic muscles arising beneath the sterno-tracheal muscles and inserted onto the first bronchial semiring ; the bronchidesmus only commences at about the level of the fourth or fifth bronchial semiring ; anteriorly, therefore, there is a free communication between the upper and lower surface of the bronchi: the first two bronchial rings are more or less ossified and closely connected with each other and with the preceding tracheal rings; the latter undergo no modifications such as those which exist in the Storks, but are of uniform thickness, closely Fig. 2. Syrinx of Abdimia sphenorhyncha. applied and often ossified. The foregoing account does not of course pretend to be a detailed description of the syrinx in the two families, but it is sufficient to indicate the main differences and to serve as a basis for comparison of them with tbe syrinx of Xenorhynchus sene-galensis and of Abdimia sphenorhyncha, which are in some respects intermediate between the two types. In Xenorhynchus there is a transition to the Ardeine syrinx in that the upper rings of both bronchi are incomplete and are (fig. 3) closed by membrane on the inner side. It appears therefore that the syrinx of Xenorhynchus agrees with that of other Storks in the peculiar arrangement of the lowermost 1 See F. E. Beddard, " A Contribution to the Anatomy of Scopus umbretta," P.Z.S. 1884, p. 543. |
