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Show 294 ON THE ANATOMY OF PHAETHON. [Feb. 16, would have to be ignominiously expelled from the Order. This catastrophe is averted by Fregata, the skull of which, as will have been gathered from the foregoing remarks, serves to link Phaethon with the Cormorants, Gannets, and Pelicans. The Steganopodes are always spoken of as Desmognathous birds. But can Phaethon, be accurately termed a desmognathous bird ? This altogether depends upon the definition of the term desmognathous. Huxley, its inventor, defined1 the condition of Desmo-gnathism as follows :-" In these birds the vomer is often either abortive, or so small that it disappears from the skeleton. When it exists it is always slender and tapers to a point anteriorly. The maxillo-palatines are united across the middle line, either directly or by the intermediation of ossifications in the nasal septum." As to the vomer of Phaethon, it is pointed in front, as is that of most Schizognathous birds ; this character does not distinguish the Schizognathas. But, as already mentioned, it diverges behind into its two component halves, in a way that is unusual among Desmognathous birds. It occurs, however, in the Herons (not in Scopus), which are admittedly allies of the Steganopodes. In Schizognathous birds, on the other hand, this bone is commonly divided behind. This part of the palate in Phaethon is in fact remarkably like that of a Grebe (cf. figs. 3 and 5). Nor does the resemblance cease here. Phaethon is really no more desmognathous than is HZchmophorus, if we apply the term as Huxley applied it; for the maxillo-palatines in both are widely apart, the vomer lying between them. In front of the maxillo-palatines, however, in Phaethon the bony palate forms a continuous platform. If this constitutes desmognathism (which it does not, be it observed, according to the definition of Huxley), then Coraclas, Eurgstomus, Jacamerops, &c, in which birds there is a considerable vacuity in front of the conjoined maxillo-palatines, are not desmognathous ; while the skulls of Geclnus viridis and Dendrocopus major (at most only just separable generically) must in that event be referred to different categories ; since in the former there is a palatal platform, and in the latter not. In Pelecanus and Phalacrocorax, Huxley has figured fused maxillo-palatines. These consist in the latter genus, in Plotus, and in Sulci of a thick mass of bone running upwards towards the roof of the skull. Their direction is quite different from the horizontally disposed maxillo-palatines of Phaethon. The conditions observable in the base of the skull of Fregata appear to m e to clear up this somewhat puzzling discrepancy. In Fregata (see fig. 4, p. 293), we have both the horizontal maxillo-palatines of Phaethon, separated from each other in the middle line as in that genus, and the obliquely running "maxillo-palatines" of Phalacrocorax. As co-existence undoubtedly disproves homology, it seems to follow that true maxillo-palatines, comparable to those of other birds, are wanting in Sula and Phalacrocorax: and if we are to 1 " On the Classification of Birds &c," P. Z. S. 1867, p. 435. |
