136 Dr Knox on the Anatomical Structure of the 
p,nd for the existence of muscular fibres, after these have ceased. 
JBoth are also common to the New Holland Cassowary, whose 
jtrachea is much larger and longer than that of the Indian. : In 
the former, likewise, at the fifty-second ring, counting from the 
glottis, there is found a large muscular bag, about the size of 
^ man’s head, into which the windpipe opens, by a large orifice, 
occasioned by a deficiency of a part of the circumference, in 
about thirteen tracheal rings ; or rather, the rings, instead of 
closing around, to form the tube of the trachea, expand out- 
wards, and are attached to the sides of the bag. This most re- 
markable, and, so far as I know^ unique structure, attracted a 
good deal of my attention. It has no communication with any 
of the air-cells. I was at first at a loss to conjecture the use of 
this bag, and its importance to the animal ; but reflecting on the 
nature of the country in which the emeu is found, it seemed to 
me extremely probable, that Nature, ever watchful of all her 
works, may have superadded this muscular appendage to the tra- 
chea of the New Holland Cassowary, to preserve it amidst those 
dangers, from sudden floods, to which New Holland is particu- 
larly exposed. The sandy plains of this extraordinary country 
are, during a great part of the year, inundated, and become then 
boundless marshes ; and the plains generally are exposed to sud- 
den inundations. The rivers, inoreover, running westward from 
the great chain of mountains, terminate in vast muddy plains or 
inland marshes. The emeu, forced to seek his food amidst 
these fens, may, when obliged to have recourse to swimming, 
(which must very often be the case,) fill the muscular bag of 
the trachea with air, and thus convert it into a swimming-blad- 
der. It may also assist the bird in escaping A’om his pursuers : 
but on this I mean not to insist, as the organ is wanting in the Ga- 
leated Cassowary, and in the ostrich ; both remarkable for speed 
of foot. A- moment’s reflection must convince every one, that 
the bag can only be filled by the expiration of the bird, and that 
it cannot be dilated by inspiration ; or, at least, it is excessively 
difficult to imagine how inspiration could be prolonged to such 
an extent, as to fill the air-cells of the body, the lungs, and mus- 
cular appendage of the trachea. On the other hand, the bird 
has only to employ the mechanism by which he forces the air 
into the air-cells and the osseous cavities, i. e. by closing the 
