LARYNX OF BIRDS.] 



UNDULATORY FORCES. ACOUSTICS. 



291 



In the monkeys of the old continent, there are also 

 laryngeal aa.cs. These sacs modify the quality of the 

 voice, giving to it, even when acute, a peculiar hoarse- 

 ness. In the Simla appetta and Simla capucina, there 

 are some peculiarities in the structure of the channel 

 for the passage of air. The voice, in quality, is like that 

 of a flute ; hence these are called whistling apes ; and, 

 from the peculiar expression of this whistle, which is a 

 plaintive melody, they are termed weeping apes. 



Voice of Birds. The great peculiarity in the organs 

 of voice, among birds, is the inferior larynx ; that is, 

 birds, in addition to the larynx corresponding to that 

 possessed by mammals, have one peculiar to themselves, 

 at the inferior extremity of the windpipe. Even the 

 superior larynx of birds differs considerably from the 

 larynx in mammals. The superior larynx, like that of 

 mammals, is placed just below the hyoid bone. It is 

 partly cartilaginous and partly osseous. In the superior 

 laryux of birds there are cartilages corresponding to 

 the thyroid and the cricoid, the two arytenoid, and the 

 epiglottis. The cricoid is much less developed than in 

 mammals ; it forms but a small portion of a ring, occu- 

 pying the posterior part of the larynx, and supporting, 

 as in inammals, the two arytenoid cartilages. The thy- 

 roid cartilage, consequently, rests on the first ring of 

 the windpipe. To the posterior margins of the thyroid 

 cartilage are connected two quadrilateral bones, by which 

 the extent of the protection afforded by the wings of the 

 thyroid cartilage is much increased. The arytenoid car- 

 s are long, and taper upwards and downwards ; 

 form, by their inner margins, the chink of the 

 glottis. They are generally ossified ; their external 

 margins are bounded by the thyroid cartilage. The 

 epiglottis, in most birds, is rudimentary, and generally is 

 Fig. 25. osseous. The chink of the glottis in birds 

 is triangular, the apex being directed up- 

 wards. It is bounded in front by the thy- 

 roid cartilage ; on each side by the arytenoid 

 cartilages ; and behind by the cricoid car- 

 tilages ; but it has no salient membranous 

 lamin;e, such as the vocal ligaments in 

 man and mammals have. It is capable of 

 expansion and contraction under the ac- 

 tion of several muscles. The inferior 

 larynx is, as we have seen, peculiar to 

 birds. (See Fig. 25). It varies very 

 much in form and structure. This larynx, 

 the vocal instrument of birds, is a tube, 

 at the opening of which is a membranous 

 tongue. This tongue is a doubling of the 

 interior lining of the bronchus, its free 

 rin*LAKTiix margin being directed upwards ; and birds 

 have, for the most part, a smaller or 

 greater number of muscles, capable of shortening this 

 tongue, or of lengthening it in the direction of its 

 hniLjht, and of rendering it tense or lax in a trans- 

 verse direction. 



In general, the inferior larynx of birds is produced 

 by a membrane which makes a projection on each side 

 of the inferior orifice of the windpipe ; this orifice is 

 divided into two apertures, sometimes by an osseous liar 

 passing from before backwards, sometimes merely by the 

 angle of union between the two bronchial divisions of 

 the windpipe. The bronclii are not composed, like the 

 windpipe, of complete rings, but merely of osseous or 

 cartilaginous segments of rings, of a greater or smaller 

 number of degrees in extent, each having a proper 

 curvature in the state of rest, which curvature may vary, 

 to a certain amount, by the action of voluntary muscles. 

 It hence follows, that the portions of the walls of the 

 two bronchial divisions of the windpipe, adjacent to 

 (that is, looking towards) each other, are, for a greater 

 or smaller extent, membranous, being there destitute of 

 any osseous or cartilaginous structure ; and it is to this 

 usually large portion of the wall of each bronchus 

 that Cuvier gives the name, tympaniform membrane. 

 Thus two tympaniform membranes descend, looking to- 

 wards each other from the angle at which the windpipe 

 divides, forming the interior wall of each of its subdi- 



1CT10* OF 1!C- 



visions, and being extended transversely between the 

 anterior and posterior extremities of the upper osseous 

 segments of the same subdivisions ; these osseous seg- 

 ments extending only along the posterior, the external, 

 and anterior part of their wall, so as to leave the inner 

 part of each bronchus simply of a membranous structure. 



The first osseous segment of each bronchus has much 

 the same curvature as the windpipe itself ; but the second 

 and third are portions of larger circles, and are less 

 convex exteriorly than the first, so that the latter pro- 

 ject on the inner side of the tube. 



On this interior projecting part, the lining membrane 

 forms a fold ; and it is this fold, half shutting one of the 

 inferior apertures of the windpipe, which olfers to the 

 air issuing forth, a tongue capable of vibrating and of 

 producing sound. 



The inferior larynx of singing and some other birds, 

 in which the voice is far from musical, is very compli- 

 cated. The last rings of the windpipe unite into a 

 structure two or three lines in length, nearly cylindrical 

 above, and expanded below, where it has two obtuse 

 points one anterior, another posterior joined by the 

 bony bar passing from before backwards, already spoken 

 of more than once. This bar is so placed that the wind- 

 pipe opens below by two oval holes, making with each 

 other an obtuse angle ; and each of these holes commu- 

 nicates with one of the bronchi. 



The three first osseous segments of each bronchus are 

 moie near to each other, and flatter, than those which 

 succeed them. From the first to the third there is a 

 gradual elongation behind, so that the posterior extre- 

 mity of the last makes a sort of projection, owing to 

 the sudden diminution of the fourth segment. The arc 

 which these segments form hardly exceeds 00 ; and in 

 each bronchus, the cord of this arc, so to speak, is the 

 tympaniform membrane. The first segment of each 

 bronchus curves its anterior extremity towards the inner 

 surface of the tube, where it articulates with a small 

 oval artilage which is fixed to the tympaniform mem- 

 brane ; while it forms within, a prominence which is the 

 vibrating lamina of the larynx on that side. Thus the 

 transverse section of each bronchus is below nearly 

 circular ; the section higher up becomes the segment of 

 a circle, which diminishes in one direction while it 

 enlarges in another ; and the passage of the air, upwards 

 into the windpipe, takes place by two oval holes, each 

 furnished at its anterior border with a salient lamina. 

 This apparatus is supplied with ten muscles, five on 

 each side. 



Of these, one descends from the interior of the wind- 

 pipe to the anterior extremity of the third segment of 

 the bronchus ; anil, by its contraction, draws that point 

 upwards, thereby making the vibrating lamina project 

 further inwards, and, at the same time, rendering tense, 

 lengthwise, all that part of the tympaniform membrane 

 lying below the segment to which the muscle is at- 

 tached. Another muscle, parallel to this, has nearly 

 the same attachments, and a like office. A third muscle, 

 much smaller, extends from the inferior and posterior 

 part of the windpipe, and is inserted into the posterior 

 extremity of the second bronchial segment. Its action 

 is similar to that of the former. A fourth muscle passei 

 obliquely from the windpipe to the posterior extremity 

 of the second bronchial segment. It draws that segment 

 upwards and outwards, so as to aid the action of the 

 muscles already referred to, and of that which follows. 

 The fifth mascle is no longer than the preceding, but is 

 much thicker. Taking its origin from the last ring of 

 the windpipe, it passes downwards and forwards, and is 

 inserted into the anterior extremity of the first bron- 

 chial segment, and particularly into the minute cartilage 

 already mentioned as being articulated with that point. 

 Its chief action .is to draw forward the small cartilage, 

 and consequently to put forcibly on the stretch, in a 

 ;ransverse direction, the upper part of the tympaniform 

 membrane. 



Such a complex structure of the iuierior larynx be- 

 longs, as was hinted at, not only to singing birds 

 such as the nightingale, the wren, the blackbird, the 



