18G7.] 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 my 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, super- 

 fluous 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 tlie 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'.). Each end is nar- 

 rowed shghtly 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 repre- 

 sented 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 (fig. 1), 



* Since the reading of this paper, Prof. Alfred Newton, of Cambridge, has di- 

 rected my attention to, and witli his accustomed courtesy forwarded me, vol. vi. 

 of the 'Naturalist' magazine (185C), 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 extends 

 along ten of the rings and dilates at each extremity." 



