VOICE 



1499 



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. dangula. 



The A.rufina, or red-breasted whistling duck, 

 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 

 Mergus Merganser. A. muscatus, A. Pcnc/ojx-, 

 or widgeon, and A. JEgyptiaca, have also bony 

 enlargements of the inferior larynx ; but the 

 Anser domesticus, and the Larus, 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 Gallinaceae the structure of the in- 

 ferior larynx is more uniform, simple, and 

 symmetrical than in the Palmipedes. In the 

 male Phasianus gal/us, 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 

 Gallinaceae, 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 Sylviadae, 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 Gallinaceae 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. 



In the Falcons, the larynx being provided 

 with but one pair of muscles, viz. the sterno- 

 tracheal. its structure is much more simple 

 than in the singing birds. The membrana 

 tympani is however large, but does not appear 

 to give off any semilunar membrane. The 

 bronchial rings are distant from each other, 

 and bound together by thin membranes ; the 

 rings of the larynx are almost in juxtaposition, 

 leaving no vibratile membranous space be- 

 tween them ; consequently the nirinbrana 

 tympani is the chief vibrating tissue. The 

 order also has one pair of vocal muscles. 



Scansores. In the parrots the inferior 



* The exceptions in this order are the Velvet 

 duck, the Golden Eye, the Red Breasted Merganser, 

 and Ganet, in which there are two pairs. 



