494 DR. R. O. CUNNINGHAM ON THE ANATOMY 
skeletons of the volant individuals to present unequivocal traces of immaturity, while, 
on the other hand, those of the non-volant were constantly found to be fully ossified. I 
believe, therefore, that as the bird increases in size and weight, owing to the deposition 
of an increased amount of mineral matter in the bones and various other causes, it 
gradually abandons the habit of flight, finding that the speed with which it can progress 
through the water by means of the rapid movements of its wings, together with its 
diving-powers, are sufficient to preserve it from threatened danger. 
As I have very lately described the habits of the Steamer Duck, I shall not occupy 
the time of the Society by recounting them, but pass on to its anatomy. Owing to the 
difficulty of carrying on prolonged dissections on board ship, and the small amount of 
room at my disposal, which prevented me from preserving entire specimens of so large 
a bird in spirits, I much regret that I was unable to work out the anatomy of the soft 
parts; so that my observations upon them are very incomplete. So far as my cursory 
inspection of the muscular system extended, I did not observe any noteworthy pecu- 
liarities. The various muscles acting on the shoulder-joint and those of the leg were, 
as might be expected, very strongly developed. The length of the @sophagus was 
nineteen inches, and that of the entire intestinal canal fourteen feet two inches. The 
stomach, as may be seen from the figures, was extremely strong and muscular, so as to 
be admirably adapted for grinding down the shells of the mussels (J/ytilus chilensis and 
M. magellanicus) and other lamellibranchiate mollusks which form the principal aliment. 
The czeca are six inches long, and their origin is at the distance of five inches from the 
anus. The trachea is very strongly formed, and only very slightly compressible, owing 
to the complete ossification of its rings. That of the male is provided with a strong, 
bony dower laryna, situated between the origin of the dronchi and the insertion of the 
sterno-tracheal muscles. The Jronchi in the female, in which no bony enlargement 
exists, are wider than they are in the male. In length the trachea measures about 
eleven inches and a half. 
Osteology. 
Fully to describe all the specific peculiarities of the skeleton of the Steamer Duck 
would necessitate a much more minute acquaintance with the subject of bird-osteology 
than I can pretend to possess, as well as a much more extensive examination of the 
bones of allied species than it has been in my power to institute. I must accordingly 
content myself with the indication of those points which appear to me to be most 
worthy of note, and crave the indulgence of the Society for the meagreness of my 
descriptions, which I have endeavoured to illustrate and supplement by means of the 
accompanying sketches. 
The materials at my disposal in drawing up the following notes have been as 
follows:—Ist, two nearly entire skeletons of adult individuals from the Falkland 
Islands, in the Museum of the Royal College of Surgeons, for permission to examine 
which, in common with the other skeletons of Anatide in that collection, I am indebted 
