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tion of the general bag of the stomach, which has no gastric glands, is much larger in the cassowary of New Holland, than in the Indian cassowary; or, in other words, the glandular crop approaches much nearer the gizzard in the latter than in the former. The gizzard is weak in both. I consider this as a character distinguishing these birds from the ostrich. It is true, that they must long since have ceased to be fed agreeably to their natural disposition; and this, according to the opinions of Mr Hunter, may have had some effect in diminishing the muscularity of the gizzard. I must suppose it owing to the same cause, that the gizzard of the ostriches I have dissected on their native desarts, always appeared to me very muscular, whilst others, who have examined the same bird, after being long in a state of captivity, describe the gizzard as not being remarkably so. It must, however, be evident to all, that the ostrich is strictly graminivorous, whilst the food of the cassowaries of India and New Holland is, without doubt, chiefly composed of insects and reptiles. The proportional lengths of the intestinal tube, in feet and inches, are as follows:

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Galeated Cas-3 8.72 4 7.35 0 5,82 0 10.63 6 5.95 sowary.-Cuv.

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In both birds the coca resemble each other closely; they are very small, and the orifices by which they penetrate the intestines are so narrow, that air blown into the intestines cannot be forced into the cœca: their parietes are thin and delicate, and they con

tain a fluid matter differing very much from the usual contents of the intestinal tube. The form of the gizzard, and of the intestinal tube generally, I have described in a note below*. The cloaca seemed to be formed much as in the ostrich, and to serve as a reservoir for the urine only; the rectum opening into it by a comparatively small orifice. The external opening of the oviduct in the Emeu of New Holland presented a circular range of membranous folds, which were wanting in the Indian Cassowary. In the latter, the hepatic canal is inserted along with the cystic and pancreatic ducts into a small bag, adhering to the intestinal canal, formed of the same tunics as the intestine itself. In the New Holland Cassowary, the hepatic and cystic ducts enter, as in the other, separately, but the small bag described above is wanting. The gall-bladder is wanting in the ostrich: the Galeated Cassowary has it of an oblong shape, and very large; it was quite filled with a dark green bile. In the New Holland Cassowary the gall-bladder is remarkable, both as to shape and strength. It is as it were divided into two portions; the parietes are strong and dense. The same may be said of the cystic duct, which bears no resemblance to the hepatic. The ducts conveying the bile from the liver to the gall-bladder enter by the fundus, and are very short. I am not aware of any physiological reason to account for these remarkable differences in birds so nearly resembling each other.

The heart of the Emeu of New Holland is more elongated than that of the Indian Cassowary; and some of its great arteries had undergone that change into semi-ossified plates, found so frequently in the arteries of the human subject, when aged. The Indian Cassowary has long been remarkable for the continuation of the cartilaginous rings of the bronchia into the lungs themselves,

In the Indian Cassowary, the duodenum is very large, but contracts gradually to the insertion of the biliary ducts. From this point, the intestine continues to diminish in caliber, to within a few inches of the insertion of the cœca. It then rapidly, though not suddenly, increases to its final termination in the cloaca. In the New Holland Cassowary, the duodenum suddenly dilates into a considerable bag, and as suddenly contracts; the intestine continues to do so for about 16 inches, when it dilates on approaching the hepatic ducts. From this point, the intestine preserves a considerable uniformity of appearance, till it approaches the insertion of the cœca, when it rapidly increases to a very great diameter. The aperture by which the rectum communicates with the cloaca is of moderate size.

and for the existence of muscular fibres, after these have ceased. Both are also common to the New Holland Cassowary, whose -trachea 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 a 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 outwards, and are attached to the sides of the bag. This most remarkable, 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 trachea of the New Holland Cassowary, to preserve it amidst those dangers, from sudden floods, to which New Holland is particularly 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 sudden inundations. The rivers, moreover, 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-bladder. It may also assist the bird in escaping from his pursuers: but on this I mean not to insist, as the organ is wanting in the Galeated 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 muscular 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

glottis, and compressing the chest. On doing this, and calling into action the abdominal muscles, the air must of necessity be forcibly driven into the bag of the trachea; and may, by retaining the glottis shut, be alternately circulated between the lungs, air-cells, and bag of the trachea, giving the bird an additional advantage in running. It may not be altogether uninteresting to add, that the contents of the stomach shewed that these birds had been chiefly fed on animal fat.

EDINBURGH,

April 1823.

ART. XXII.—Additional Observations on the Structure of the Trachea in the Cassowary Emeu of New Holland. By Dr ΚΝΟΧ.

IN the preceding paper, I have detailed, at considerable length,

the peculiarities in the internal structure of the Cassowary of New Holland, and of the Indian Emeu or Cassowary, describing, at the same time, though somewhat briefly, a very remarkable appendage of the trachea in the former bird, which had escaped the notice of preceding comparative anatomists. Since that time, frequent inquiries have been made, in relation to this peculiar structure; more particularly as to its nature, supposed functions and importance; but chiefly as to its analogies with the appendages found in the trachea of several other birds, of the duck and merganser kind. Now, these inquiries convinced me, that the subject had been viewed very incorrectly, even by those who were good anatomists, but who had not themselves examined the anatomy of the windpipe of birds, and had merely read accounts of the appendages sometimes connected with them; and this is the excuse I offer, for again recurring to this subject. I shall now briefly point out (what ought to have been done formerly) the total dissemblance between the appendage of the trachea in the Cassowary of New Holland, and those found in any other animal.

With a view to be better understood by those gentlemen who are not quite conversant with anatomical subjects, I shall refer to specimens of the trachea of the peacock, singing swan

(Anas Cygnus,) the golden-eyed duck (Anas clangula,) the Cassowary of India, and that of New Holland; of some of which I have caused accurate drawings to be made. In these, though diminished to about a sixth, the proportions have been strictly observed. It will be necessary, therefore, only to recall to the recollection a few elementary ideas, in order to place the subject in its true light.

In birds the trachea is, generally speaking, proportioned to the length of the neck, hut to this there are some remarkable exceptions, the chief of which, as far as I have observed, is found in the Anas Cygnus, or wild swan. Moreover, in birds generally, the cartilaginous rings or circles of the trachea or bronchia (which in the trachea are complete), are found of equal diameter nearly throughout; but to this, also, there are some exceptions. Several present one or more dilatations in the course of one or other of these canals, and the actual diameter of the cartilaginous circles varies either gradually or suddenly. These peculiarities in structure are found chiefly in swimming birds, and one of the most remarkable is that which I now present to the Society. It would be difficult to decide on the precise use of these dilatations of the trachea in the swimming birds; but as they seem to be generally found in the male only, it is not improbable that they are connected with the organs of voice. But in the Cassowary of New Holland, the structure of the appendage of the trachea is altogether dissimilar to those described. It may be recollected, that in this bird the rings of the windpipe are complete, from their commencement at the upper larynx to about the fifty-second, when the next rings suddenly open by a wide aperture into a strong muscular bag, as large as the human head, closely attached to the sides of the trachea, and expanded rings. This bag is situated in the neck, immediately above the bone called Merry-thought: it was seen by me in the female, though it is probable that the male also possesses it. It is quite peculiar to the bird, no such appendage having been ever seen attached to the trachea of any of the feathered creation; nor do I know of any thing analogous to it in any other animal, excepting in the cameleon, to the upper portion of whose trachea there is appended a comparatively large membranous bag.

I stated in my former observations, that I believed it to per

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