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Show 1876.] ON THE ANATOMY OF CHAUNA DERBIANA. 189 3. On the Anatomy of Chauna derbiana, and on the Systematic Position of the Screamers (Palamedeidce). By A. H. G A R R O D , M.A., F.Z.S., Prosector to the Society. [Received January 5, 1876.] (Plates XII.-XV.) In his memoir "on the systematic position of the Crested Screamer (Palamedea chavaria)," published in the * Proceedings' of this Society*, Prof. Parker has placed that bird among the An-seres, and away from the Rallidae, with which it had been generally associated. In his "Classification of Birds"f, Prof. Huxley adopts the same view as Prof. Parker. Both these distinguished authorities base their opinions on anatomical considerations ; it therefore behoves me to attempt to substantiate the different views expressed by me in m y paper " on certain muscles of Birds, and their value in Classification "J, as it is so considerably at variance with that of the authorities just mentioned. The great extent to which the skeleton is permeated with air renders the features presented by the different bones of Chuna less distinctive than in the majority of birds. For this reason the soft parts will be first considered. Cutaneous System. Pterylosis.-Nitzsch has described the pterylosis of Palamedea cornuta and Chauna chavaria; and, as might be expected, C. derbiana does not differ in any important particulars from the latter. As he remarks, the most striking point observed in the plucked bird is the extreme whiteness of the surface, which depends on the fact that the skin is almost universally emphysematous to the depth of nearly a quarter of an inch. On pressing with the finger, the characteristic crackling of a tissue filled with air is most marked, the only places in which it is absent, or nearly so, being the anterior surfaces of the upper ends of the tibia, and, to a less degree, two triangular spaces, equilateral, with their bases towards the middle line, situated one on each side over that part of each pectoral region which is near the head of the humerus, in the apex of the larger triangular surface bounded by the superior and axillary margins of the great pectoral muscle. Iu the Gannet and the Pelican the skin is likewise emphysematous, but not exactly in the same way. In them the superficial surface of the cutis forms a plane surface, and the deep layer another, with the air-cells intervening between them, and the feather-quills traversing them. In Chauna, however, these two cutaneous layers are not definable, the whole presenting the appearance as if a non-emphysematous skin had been forcibly blown up, so as to cause its surface to be irregular and bubbled, more like an artificially distended mammalian lung than any thing else. The feathers and the semiplumes do not perforate the air-cells, but cause the skin to he indented where they are situated. * P.Z.S. 1863, p. 511. t P.Z.S. 1867. p. 415. \ P. Z. S. 1874, p. 117. |