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Show 1867.] DR. J. MURIE ON THE EMU. 407 and the preparation with the distended sac is shown from behind. Carus's figure, of natural size and from an adult bird, only displays the profile contour of the tracheal expansion. I bring the present paper before the Members of our Society, partly to give a figure supplying the deficiency just alluded to*, and partly to add fresh observation of facts connected with the size of the sac in the young and old birds, with additional remarks on its probable use. Structure.-I have been enabled to examine, in all, three birds, which from time to time have died in the Society's Gardens,-the first an adult male, in which, unaware of the nature of the opening in the trachea, I had grave doubts that it might have been occasioned by faulty manipulation with the scalpel on m y part. I, however, took a photograph of the portion of the trachea and its deficient anterior chink, which I exhibited at the meeting of the Society. The second bird was an adult female. In this case I carefully examined the trachea in order to ascertain whether the tracheal opening was a natural condition. I subsequently made myself acquainted with the labours of previous observers. The third bird was a young male, and in this I found a very great difference in the size of the sac compared with the older birds. The descriptions of the several investigators spoken of corroborate each other in the main, and to some extent agree with what I have also seen in the adult Emu. I should consider it, therefore, superfluous to redescribe the entire structure, were it not that it enables us to compare the condition of the sac in the old and the young bird, and allows some part of the mechanism to be more fully explained. In the adult female dissected by me the sac was of large size, and occupied the lower and anterior surface of the neck, its lower end reaching close to the sternum. Its exact shape when distended I did not ascertain ; for, thinking I should be able to reflect the skin and tissues covering the bag previous to inflation, I accidentally cut into it while attempting this, the superincumbent coverings and its own walls being very thin. The sac when opened presents an oblong cylindrical form (as shown in fig. 1, T.p. T.p'i). Each end is narrowed slightly and comparatively fixed, while the middle portion is freer, thus permitting a certain amount of outward expansion, from the anterior deficiency of the tracheal rings. This no doubt would give it a more oblate spheroidal form when blown up. In Knox's figure, where the sac and trachea are seen from behind, it is represented as being of a globular shape. The trachea in his woodcut appears considerably broader at the sac than above or below, because of the distention of the parts. In the accompanying woodcut (flg. 1), * Since the reading of this paper, Prof. Alfred Newton, of Cambridge, has directed m y attention to, and with his accustomed courtesy forwarded me, vol. vi. of the 'Naturalist' magazine (1856), where in the July number, p. 153, is a " Notice of a peculiar Organ in the Trachea of the Emeu," communicated by Mr. Robert Anderson. Two woodcuts accompany the short paper, and one of these exhibits the tracheal chink; but both are very poor representations, and convey no idea of the mechanism of the parts. The author states " the opening extend* along ten of the rings and dilates at each extremity." |