In the female the larynx is of a much simpler structure, the external wall is com posed of several consolidated rings, those situ ated below the os transversale terminating in the membrana tympaniformis between the last bone of the larynx and first of the bronchus.
In the Anas clangula we find another variety in the structure of the vocal organs. The inferior larynx is nearly of a semilunar form, with its convex surface directed exteriorly ; it is situated obliquely to the axis of the trachea. It is partly bony, and partly mem branous, and divided into several cavities. A large semilunar bone forms the principal framework of the whole larynx. On the left side there are two cavities, one of which is situated above the other. The superior cavity is formed by a groove in the semilunar bone by which it is bounded both externally and in ternally, but is furnished with a membrane above. At the posterior extremity of the bone forming the floor of this cavity, there is a perforation by which the air in the inferior cavity from the left bronchus is admitted. The inferior cavity lies at the base of the larynx, and is connected with both bronchial and tracheal apertures ; it is bounded an teriorly by the semilunar bone, and inferiorly by the basilar membrane.
On the right side the semilunar bone forms externally a protuberance, which is concave within, forming the anterior and lateral bound ary of a large cavity which lies between the bronchial and tracheal apertures. This cavity is subdivided by bone and membranes into two irregularly formed cul de sacs, which are nearly parallel to the axis of the trachea.
The os transversale is a very irregularly formed bone, as in the Mergansers, dividing the larynx into two unequal and unsymmetrical parts ; its superior prominence, which is conical, penetrates the trachea nearly one eighth of the entire length of that tube. The rings of the trachea here are no longer entire but divided anteriorly and posteriorly by a dense membrane, and in some places by os seous interposed substances, the whole being supported within by the os transversale. A basilar membrane supported by the semilunar bone, forms the floor of the larynx. This membrane is perforated by the bronchial tubes, and is connected with the bronchi by means of the membrana tympani. In the female, the left side of the larynx lies above the right, as does that of the male, and the base is like wise oblique to the axis of the trachea. The trachea of the male has an enlargement occu pying about one-fourth of its length, its size being regulated by an additional pair of mus cles, which draws the rings of that part either into an oblique, or into a nearly horizontal position.
The whole of this complicated mechanism is concerned in producing the tones peculiar to the A. clangula.
The A.rufina, or red-breasted whistling cluck, presents another instance of laryngeal struc ture peculiar to itself; but our limits will not admit our giving its anatomy in detail : let it suffice therefore to mention, that its left cavity, which is largest, is chiefly membranous, whilst the right is almost entirely osseous, and some what resembles in external form the larynx of 21fergus Merganser. A. muscatu,s, A. Penelope, or widgeon, and A. ./Egypliara, have also bony enlargements of the inferior larynx ; but the Anser domestieus, and the Lams, and Ardea, with some others amongst the Grallatores, are destitute of these enlarged cavities common in the order Anas. The organs of voice in the Palmipedes are, with a few exceptions, only provided with one pair of muscles.* In the Gallinacem the structure of the in ferior larynx is more uniform, simple, and than in the Palmipedes. In the male Phasianus gallus, the common cock, this larynx is composed externally of two or three of the lower half rings of the trachea, con nected in the inside with the os transversale both anteriorly and posteriorly, through the interposition of two triangular laminas given off by it, which are also connected with the bronchi. Between the rings of the larynx there is interposed a membrane which forms the side of the glottis externally. The inferior portion of the trachea is much com pressed laterally. The inferior larynx of the pheasant does not differ materially in structure from that of the cock. In the partridge the os transversale is attached immediately to the last half ring of the larynx. In the owing to the os transversale lying below the last semilunar rings of the larynx, the membranes on each side are immediately opposite to each other, so as to form the two sides of the glottis, and the larynx is not en tirely a double reed as in the Sylviadm, in which the membrana semilunaris forms with the membrana tympani the interior lips of the glottis, and divides the larynx into a double organ of voice. In this respect the structure of the larynx in the Gallinacem is intermediate between the parrots and the singing birds. The trachea being compressed laterally, and the glottis very straight, these, according to Cuvier, may be considered the causes of the acute sounds which these birds produce. They are provided with one pair of muscles. In the Indian pigeon, however, the sterno tracheal muscles divide, and send a few fibres to the inferior larynx.