333 



LARYNX. 



LARYNX. 



334 



Fig. 10. 



of the larynx. They are formed of elastic tissue, like the inferior or 

 true vocal ligaments, but in less quantity, and mixed with fatty tissue, 

 so that they do not vibrate so freely. The walla of the ventricle are 

 capable of being approximated by some of the fibres of the thyro- 

 arytenoid muscles, which are thinly distributed upon them ; and thus 

 the recess may be nearly obliterated, 

 and the upper ligaments brought 

 almost into contact. 



The highest part of the larynx is 

 formed by two folds of membrane 

 passing from the arytenoid cartilages 

 to the epiglottis (fig. 10), forming 

 an oval aperture which admits of 

 variations of size by the action of 

 the muscles already mentioned. At 

 this aperture the larynx communi- 

 cates with the upper and most ex- 

 panded part of the pharynx, the 

 cavities of the mouth and nose, and 

 the frontal and other sinuses which 

 open into the latter. These sinuses 

 nix- I led mund l>y bone, but tliij 

 pharynx and its communications with 

 the mouth and nose, as well as the 

 external apertures of the two latter 

 cavities, are in great part muscular, 

 and may be thus subject at will to 

 alterations of form, size, and tension. 



The larynx has been compared to 

 a variety of musical instruments, and 

 it will be seen tuut in its different 

 parts it unites the principles of seve- 

 ral. In its essential vocal apparatus 

 it most nearly resembles the reed- 

 instruments, as the reed-pipes of the 

 organ, the clarionet, &.C., or rather a 

 modification of them, in which the 

 vibrating body is not fixed in its 

 dimensions as a metallic tongue, or 

 a reed, but consists of a lamina of 

 elastic membrane, capable of varied 

 degrees of tension, as well as of altera- 

 tions in its length. No musical in- 

 strument has yet been constructed 



on this principle, unless we consider cartilage; S, 3, Cricoid cartilage; 

 as such the various kinds of trumpet 4,4, Arytenoid cartilages ; 5, Epi. 

 in which the vibrations are produced glottis ; 6, Aperture of communica- 

 by the air impelled against the edges ion between glottis and pharynx ; 

 of the lips, rendered more or less 7 - ' Rin &" of trachea i " ""nation 

 tense by the action of their orbicu- 

 U, muscle. The princip.e has been 

 applied in the formation of artificial 

 laryiiges by Biot, Cagniard de la Tour, Willis, &c., who have chiefly 

 used caoutchouc membrane ; and by Muller and Henle, who have 

 employed besides either the vocal ligaments themselves, or laminae 

 of the elastic coat of an artery. The most complete examination of 

 the subject is that made by Muller, and published in the first part of 

 the second volume of his ' Physiologic des Menschen.' 



It is evident that by adapting to one of the open extremities of a 

 tube two portions of thin elastic membrane, so that their opposite 

 edges leave a narrow space in the middle, through which the air blown 

 into the other end of the tube may pass and excite vibrations, one 

 obtains an imitation of the essential vocal apparatus of the larynx ; 

 the tracbea being replaced by the tube, the vocal ligaments by the 

 bands of elastic membrane, and the glottis by the space between them, 

 while the parts above the glottis may be imitated by adapting tubes 

 of different sizes and forms above the membranes. 



In such an apparatus Mr. Willis 

 found ( ' Cambridge Philosophical 

 Transactions,' 1832) that in order 

 that two hun i me of elastic membrane 

 inclosing a narrow interval should 

 produce sound, the parts near their 

 edges must be parallel to each other. 

 Applying this law to the case of the 

 larynx, he observes that something 

 more U necessary for speaking or 

 singing than a certain degree of ten- 

 sion of the vocal ligaments, for they 

 are always more or less tense ; and 

 even when their tension is increased , 

 and all the cartilages are in the posi- 

 tion for producing sound, we may yet 

 breathe quietly, the edges of the vocal 

 ligaments not being parallel. 



Fly. 12 represent* two vertical 

 tiansverse sections of the larynx, the continued line indicating the 

 position of it* parts when not sounding, the dotted line the same parts 



MAT. HIST. DIV. VOL. III. 



1, 1, Os hyoidea ; 5, 2, Thyroid 



" f tnul " eri>e 



Fig. 11. 



i Fig. 12. 



in the vocalising position, in which the edges of the ligaments are 

 parallel to each other. Mr. Willis considers it to be one of the func- 

 tions of the thyro-arytenoid muscle to place the ligaments in this 

 essential position. 



When the vocal ligaments are thus placed, the modulations of the 

 notes are effected by the changes in their length and tension ; for, like 

 those of other elastic membranes stretched at both ends, they follow 

 in many respects the same laws as cords. [CORD, in ARTS AND Sc. DIV.] 

 Thus, the degree of tension being the same, the height of the note is 

 inversely as the length of the membrane ; and the length being the same, 

 the height of the note, as expressed by the number of vibrations, is 

 directly as the square root of the power employed in producing the ten- 

 sion. The application of these laws to the vocal ligaments was experi- 

 mentally proved by Muller. In a part of his experiments on the dead 

 larynx he succeeded in producing the complete scale of notes and half- 

 uotes through a range of 2J octaves, by gradually increasing the tension 

 of the vocal ligaments by weights appended to one of their extremities. 

 The weights produced extension in the same direction in which the 

 crico-thyroid muscles act, when, the avytenoid cartilages being fixed, 

 they throw them backwards with the cricoid as already explained. 

 If instead of stretching the vocal ligaments they were left to their 

 own elasticity, or still more relaxed by artificial means, in imitation of 

 the action of the thyro-arytenoid muscles, still lower notes could be 

 produced. 



In the course of these experiments Muller found that the tones of 

 the dead larynx, which in the lower notes closely resembled the chest- 

 notes of the human voice, were very apt, as they ascended in the scale, 

 to assume the characters of the falsetto voice. He was thus led to 

 discover the mode in which the latter class of notes (whose origin had 

 long been the subject of great doubt) is produced. In sounding the 

 chest-notes, and in the common voice of speaking, the whole vocal 

 ligaments vibrate, and with them part of the ventricles, and of the 

 thyro-arytenoid muscles ; but in the falsetto notes it is only tbe thin 

 edges of the ligaments which are thrown into vibrations. He found 

 also that he could prevent the tones of the chest-notes from breaking 

 into those of the falsetto, as he ascended in the scale, by compressing 

 the part of the larynx immediately below the glottis, in imitation of 

 the action of the lower fibres of the thyro-arytenoid muscles. 



As in all reed-instrumento, the velocity of the current of air exciting 

 the vibrations of the vocal ligaments has an influence on the note 

 produced ; thus Muller found that the natural note of the vocal 

 ligaments at a given tension could be raised to its fifth by blowing 

 with increased force. He believes that in singing the same note with 

 varied degrees of force, a compensation is effected by lessening the 

 tension of the ligaments in the same proportion as the velocity of the 

 current is increased ; but it seems more probable that the tension of 

 the ligaments is always the same for the same note, while it is the 

 office of the epiglottis to prevent the notes from rising with the 

 increased force of the air. It may effect this on a principle discovered 

 by M. GranicS (Magendie's ' Precis de Physiologic,' i. 253), who found 

 that to remedy the inconvenience arising from the ascent of the note 

 when the current of air blown into a reed organ-pipe was increased, 

 it wns sufficient to place within the pipe directly over the reed a 

 supple elastic tongue, which shielded it very nearly in the same manner 

 as the epiglottis covers the vocal ligaments. 



Muller found that sounds were most easily produced from the dead 

 larynx when the anterior angles of the arytenoid cartilages were in 

 contact, so that only that part of the glottis was open which is bounded 

 by the vocal ligaments. The tension of the ligaments being fixed, 

 the same note could be produced whether the glottis were widely open 

 or nearly closed ; but it is probable that, though not essential, the 

 varying apertures of the glottis are auxiliary to the complete and puro 

 sounds of the different notes; for Magendie (1. c., p. 247) distinctly 

 saw it become narrower as the notes emitted by a dog were higher ; 

 and in singing high notes one clearly feels that the air passes through 

 a narrower aperture and with more difficulty than in singing the 

 low notes. 



The notes produced at the glottis are subjected to modifications in 

 timbre, strength, and purity, by the parts connected with the larynx 

 both above and below the vocal ligaments. To illustrate this, one 

 need only refer to the difference of tone which may be drawn from a 

 clarionet-reed when it is only attached to the mouth-piece, and when 

 the mouth-piece is fixed on the body of the instrument. This part 

 of the subject has been particularly illustrated by M. Savart, Mr. 

 Wheatstone, and Mr. Bishop. It is well known that in all reed instru- 

 ments, unless the tube or body be adapted to the reed so as to be 

 capable of the same number of vibrations as it is, there is always a 

 discordance of sounds. If for example the tube be unalterable in 

 length, while the reed is capable of varied modifications of pitch, the 

 sounds will be irregular in intensity, and in some parts of the scale 

 will be totally extiuguished. Thus it is that in organs, in each pipe, 

 the tongue and the tube have to be adapted to each other, and that in 

 clarionet-playing much of the perfection of the tone depends on the 

 adaptation of the pressure of the lips on the reed to the length of the 

 tube as determined by the number of holes covered by the fingers. 

 Savart ('Journal de Physiologic,' t. 5) has shown that if the walls of 

 the tube, instead of being fixed in their dimensions like those of reed- 

 instruments, be capable of varying degrees of tension, an extraordinary 



2 A 



