ORGANS OF VOICE.] 



DlSDULATOR-i: FORCES ACOUSTICS. 



281 



a, the cricoid; l, the thy- 

 roid ;,*, the epiglottis. 



convexity being directed forwards, and it may be felt 

 immediately above the great cartilage of the larynx. 

 This great cartilage, then, termed the thyroid cartilage 

 (see Fig 12) may be described as a quadrilateral shesi 

 of cartiiage, with appendages at its four angles, named 

 its cornua, or horns. This quadrilateral sheet is bent 

 alone* its perpendicular middle line, and this bending 

 constitutes the angle which is felt in Adam's apple : the 

 upper horns are attached to the hyoid bone ; the under 

 horns to the basement ring before spoken of. Inus the 

 thyroid cartilage is wrapped round the essential parts of 

 the larynx, covering them in front, leaving them exposed 

 behind. The prominent angle in front corresponds to 

 Fig. 14, an interior angle on its posterior 



aspect ; and to the middle part 

 of this interior angle extends the 

 apex of the triangle formed by 

 the vocal ligaments, and there 

 obtains an attachment. 



A movable valve, like a little 

 tongue, its apex directed back- 

 wards, is attached to the same 

 interior angle of the protecting 

 cartilage, a little higher up, over- 

 hanging the cavity of the larynx. 

 Between the same interior angle 

 of the anterior protecting carti- 

 lage, and the two movable poste- 

 rior cartilages before described, 

 muscular fibres proceed, by the 

 contraction of which those trian- 

 gular movable cartilages are 

 jr^n forwards, so as to re- 

 ^ ^ ^^^ ^^ a] re ady 



termed vocal ligaments. From the same interior 

 angle of the -protecting cartilage, an elastic substance 

 proceeds, radiating in different directions, so as to 

 close in the parts otherwise unoccupied, above the 

 lateral portions of the basement ring of the larynx. 

 This elastic substance, in particular, forms two 

 cords, extending between the superior points of the 

 movable triangular cartilages, and the sides of the tongue- 

 like valve before spoken of. These cords constitute what 

 have been termed, somewhat improperly, the superior 

 vocal ligaments. (See Fig. 13). When the space be- 

 neath these so-called superior vocal ligaments and the 

 true vocal cords, or vocal ligaments, is examined, a cavity 

 is found on eacli side of considerable extent ; and the 

 two cavities are called the ventricles of the larynx. The 

 mucous membrane, descending from the mouth and nos- 

 trils, covers and forms a lining to these parts in its 

 passage downwards into the windpipe and lungs ; so that 

 the so-called superior ligaments of the larynx are often 

 described as mure folds of the mucous membrane, ex- 

 tending between the posterior pyramidal cartilages and 

 the protecting cartilage. It appears, however, from 

 more minute investigation, that these folds of the mucous 

 membrane do actually contain an elastic substance, not 

 less capable, under certain circumstances, of vibratory 

 action than the true vocal cords, or true vocal ligaments. 

 To recapitulate, then, the prominent points in the 

 conformation of the larynx the windpipe, called by 

 anatomists the trachea, is surmounted by a complete 

 cartilaginous ring, about an inch in diameter. This 

 ring is the only outlet of the lungs by which air can 

 issue from their numerous cavities, and is the only 

 inlet by which air can penetrate from the atmosphere 

 into the same cavities. This ring, being of a firm car 

 tilaginous structure, is plainly incapable, under any 

 ordinary circumstances, of dilatation and contraction. 

 But the air is permitted neither to pass inwards, nor to 

 come forth through the whole area of this cartilaginous 

 ring, whether in respiration or in the exercise of voice. 

 Its area is closed up on each side by impervious texture, 

 go as to permit a passage to the air only by a chink, 

 variable in its size, extending in the direction of its 

 antero-posterior diameter. This chink is bounded, ac- 

 cording to the common descriptions, by the vocal liga- 

 ments, one on each side ; and at its posterior part by the 



VOL. I. 



cartilaginous processes of the base of the movable 

 pyramidal cartilages to which these cords are connected. 

 This chink, when most expanded lengthways, is about 

 eleven lines in length ; and of this space seven lines 

 lie between the vocal ligaments, and four between 

 the opposite cartilaginous bases of the pyramidal car 

 tila^es, above spoken of, to which anatomists give the 

 name of arytenoid. (See Fig. 13). This clunk, as above 

 stated, is usually described as triangular, with its base 

 between the two arytenoid cartilages, and its apex at- 

 tached to the anterior angle of the protecting cartilage, 

 above spoken of, to which anatomists give the name of 

 hyroid. (See Fig. 14). More correctly, at its greatest 

 [ilatation, it has a lozenge shape, with the posterior 

 an^le truncated. Thus the chink commences narrow 

 mmediately behind the thyroid cartilage, expands 

 >etween the vocal ligaments to their attachment at the 

 >ase of the arytenoid cartilages, and then contracts in 

 he space between the cartilaginous bases of these two 

 >odies, not to a point, but to a truncated angle. The 

 widest part of the chink, in its greatest state of dilatation, 

 s about five lines and a-half nearly half an inch. This 

 greatest degree of dilatation takes place during inspira- 

 tion; during expiration, the chink undergoes a slight 

 contraction. But during the exercise of voice, the pos- 

 terior part, bounded by cartilaginous margins, as being 

 between the base of the arytenoid cartilages, is entirely 

 obliterated. Thus it is correctly stated, that the chink, 

 concerned in the exercise of voice between the true vocal 

 igaments, at its greatest dilatation, is of a triangular 

 shape, being entirely bounded on the sides by the vocal 

 ligaments, and its base corresponding to the points 

 between their attachment to the arytenoid cartilages. 

 As before stated, the arytenoid cartilages are attached 

 to the upper surface of the posterior part of the base- 

 ment cartilage of the larynx, or cricoid cartilage (see 

 Fig. 14) ; and the vocal ligaments being attached to 

 the bases of these arytenoid cartilages, it is manifest, 

 that when these cartilages are drawn together, the vocal 

 cords must approximate ; that when these cartilages are 

 drawn asunder, the vocal cords must recede from each 

 other at their posterior part ; that when the arytenoid 

 cartilages are drawn backwards, the vocal cords must be 

 put on the stretch ; that when the thyroid cartilage, to 

 the interior of which the apex of the triangle, formed 

 with cords, is attached, is drawn forwards, they must 

 also be put on the stretch. All these changes are known, 

 to occur by the action of particular sets of muscles. 

 The thyroid cartilage, which forms "Adam's apple," is 

 connected to the basement, or cricoid cartilage, by an 

 elastic membrane, which of itself tends to keep the 

 thyroid cartilage nearly in the same perpendicular line 

 with the cricoid, so as, in some degree, to stretch the 

 vocal ligaments. But there are two muscles extending 

 between the cricoid cartilage and the thyroid, by which 

 the thyroid cartilage is drawn forwards, so as distinctly 

 to stretch the vocal ligaments. There are also two 

 muscles extending between the posterior part of the 

 cricoid cartilage, and the posterior surface of the aryte- 

 noid, by which the arytenoid cartilages are drawn back. 

 These two pairs of muscles, when they act concurrently, 

 must very much stretch the vocal ligaments. A set of 

 muscular fibres, before spoken of, passing between the 

 arytenoid cartilages on their posterior aspect, by their 

 contraction causes the cartilages to approximate. Iwo 

 other muscles, extending from the sides of the cricoid 

 cartilage to the arytenoid, draw them asunder, borne 

 other muscular fibres are found, connecting the carti 

 lages of thi larynx; but the account of these, owing to 

 their less importance, may be omitted. 



The small muscles of the larynx are represented in the 

 f oUowing figure. The crico-thyroidei (6, No 1 ; a, No. 2), 

 and the crico-arytenoidei postici (b, No. 2), extend the 

 vocal cords in the direction of their length, and, at the 

 same time, narrow the glottis. The crico-arytenoidei 

 laterales (c, No. 2), and the thyro-arytenoidei (d, No. 2), 

 rather relax the vocal cords. The oblique and transverse 

 fibres of the arytenoideus (e, and f g, No. 2) close the 

 posterior half of the glottis. The epiglottis (K, No. 2) 



