II. THE REED
I will now pass on to the consideration of the voice-box, or larynx, containing the reed portion of the vocal instrument.
Fig. 4
from Behnke's 'Mechanism of the Human Voice'
FIG. 4.—The cartilages of the larynx or voice-box. A large portion of the shield cartilage on the right side has been cut away, in order to show the two pyramid cartilages; these are seen jointed by their bases with the ring cartilage; anteriorly are seen the two vocal processes which give attachment to the two vocal cords (white ligaments), which extend across the voice-box to be inserted in front in the angle of the shield cartilage. Groups of muscles pull upon these cartilages in such a manner as to increase, or diminish, the chink between the vocal cord in ordinary inspiration and expiration; in phonation a group of muscles approximate the cords, while another muscle makes them tense.
The Larynx.—The larynx is situated at the top of the sound-pipe (trachea or windpipe), and consists of a framework of cartilages articulated or jointed with one another so as to permit of movement (vide [fig. 4]). The cartilages are called by names which indicate their form and shape: (1) shield or thyroid, (2) the ring or cricoid, and (3) a pair of pyramidal or arytenoid cartilages. Besides these there is the epiglottis, which from its situation above the glottis acts more or less as a lid. The shield cartilage is attached by ligaments and muscles to the bone (hyoid) in the root of the tongue, a pair of muscles also connect this cartilage with the sternum or breastbone. The ring cartilage is attached to the windpipe by its lower border; by its upper border in front it is connected with the inner surface of the shield cartilage by a ligament; it is also jointed on either side with the shield cartilage. The posterior part of the ring cartilage is much wider than the anterior portion, and seated upon its upper and posterior rim and articulated with [!-- pagenumber --]it by separate joints are the two pyramidal cartilages (vide [fig. 4]). The two vocal cords as shown in the diagram are attached to the shield cartilage in front, their attachments being close together; posteriorly they are attached to the pyramidal cartilages. It is necessary, however, to describe a little more fully these attachments. Extending forwards from the base of the pyramids are processes termed the "vocal processes," and these processes give attachment to the elastic fibres of which the vocal cords mainly consist. There are certain groups of muscles which by their attachment to the cartilages of the larynx and their action on the joints are able to separate the vocal cords or approximate them; these are termed respectively abductor and adductor [!-- pagenumber --]muscles (figs. [5] and [6]). In normal respiration the posterior ring-pyramidal muscles contract synergically with the muscles of inspiration and by separating the vocal cords open wide the glottis, whereby there is a free entrance of air to the windpipe; during expiration this muscle ceases to contract and the aperture of the glottis becomes narrower (vide [fig. 10]). But when the pressure is required to be raised in the air passages, as in the simple reflex act of coughing or in vocalisation, the glottis must be closed by approximation of the vocal cords, and this is effected by a group of muscles termed the adductors, which pull on the pyramid cartilages in such a way that the vocal processes are drawn towards one another in the manner shown in [fig. 7]. Besides the abductor and adductor groups of muscles, there is a muscle which acts in conjunction with the adductor group, and by its attachments to the shield cartilage above and the ring cartilage below makes tense the vocal cords (vide [fig. 5]); it is of interest to note that this muscle has a separate nerve supply to that of the abductor and adductor muscles.
Fig. 5
Diagram after Testut (modified), showing the larynx from the front.
Fig. 6
Diagram after Testut (modified), showing the posterior view of the larynx with the muscles.
On the top of the pyramid cartilages, in the folds of mucous membrane which cover the whole inside of the larynx are [!-- pagenumber --]two little pieces of yellow elastic cartilage; and in the folds of mucous membrane uniting these cartilages with the leaf-like lid cartilage (epiglottis) is a thin sheet of muscle fibres which acts in conjunction with the fibres between the two pyramid cartilages (vide [fig. 8]). I must also direct especial attention to a muscle belonging to the adductor group, which has another important function especially related to vocalisation: it is sometimes called the vocal muscle; it runs from the pyramid cartilage to the shield cartilage; it apparently consists of two portions, an external, which acts with the lateral ring-shield muscle and helps to approximate the vocal cords; and another portion situated within the vocal cord itself, which by contracting shortens the vocal cord and probably allows only the free edge to vibrate; moreover, when not contracting, by virtue of the perfect elasticity of muscle the whole thickness of the cord, including this vocal muscle, can be stretched and thrown into vibration (vide [fig. 8]). In the production of chest notes the whole vocal cord is vibrating, the difference in the pitch depending upon the tension produced by the contraction of the tensor (ring-shield) muscle. When, however, the [!-- pagenumber --]change from the lower to the upper register occurs, as the photographs taken by Dr. French and reproduced in a lecture at the Royal Institution by Sir Felix Semon show, the vocal cords become shorter, thicker, and rounder; and this can be explained by supposing that the inner portion of the vocal muscle contracts at the break from the lower to the upper register (vide [fig. 11]); and that as a result only the free edges of the cords vibrate, causing a change in the quality of the tone. As the scale is ascended the photographs show that the cords become longer and tenser, which we may presume is due to the continued action of the tensor muscle. Another explanation is possible, viz. that in the lower register the two edges of the vocal cords are comparatively thick strings. When the break occurs, owing to the contraction of the inner portion of the vocal muscle, we have a transformation into thin strings, at first short, but as the pitch of the note rises, the thin string formed by the edge of the vocal cord is stretched and made longer by the tensor. It should [!-- pagenumber --]be mentioned that Aikin and many other good authorities do not hold this view.
Fig. 7
A-A', Ring Cartilage. B, Shield Cartilage. 1, Pyramid Cartilage. 2, Vocal Process. With 2', Its Position After Contraction of Muscle. 3, Postero-External Base of Pyramid, Giving attachment to Abductor and Adductor Muscles at Rest, With 3', Its New Position After Contraction of the Muscles. 4, Centre of Movement of the Pyramid Cartilage. 5, the Vocal Cords at Rest. 5', their New Position After Contraction of the Abductor and Adductor Muscles, Respectively Seen in I and II. 6, the interligamentous, With 7, the intercartilaginous Chink of the Glottis. 8, the Arrow indicating Respectively in I and II the Action of the Abductor and Adductor in Opening and Closing the Glottis.
FIG. 7.—Diagram after Testut (modified), showing: (i.) the action of the abductor muscle upon the pyramid cartilages in separating the vocal cords; (ii.) the action of the adductor muscles in approximating the vocal cords.
Fig. 8
FIG. 8.—Diagram after Testut (modified) with hinder portion of larynx and windpipe cut away, showing the conical cavity of the sound-pipe below the vocal cords. The ventricle above the vocal cords is seen with the surface sloping upwards towards the mid line.
A diagram showing a vertical section through the middle of the larynx at right angles to the vocal cords shows some important facts in connection with the mechanism of this portion of the vocal instrument (vide [fig. 8]). It will be observed that the sound-pipe just beneath the membranous reed assumes the form of a cone, thus the expired air is driven like a wedge against the closed glottis. Another fact of importance may be observed, that above the vocal cords on either side is a pouch called a ventricle, and the upper surfaces of the vocal cords slope somewhat upwards from without inwards, so that the pressure of the air from above tends to press the edges together. The force of the expiratory blast of air from below overcomes the forces which approximate the edges of the cords and throws them into vibration. With each vibration of the membranous reeds the valve is opened, and as in the case [!-- pagenumber --]of the siren a little puff of air escapes; thus successive rhythmical undulations of the air are produced, constituting the sound waves. The pitch of the note depends upon the number of waves per second, and the register of the voice therefore depends upon two factors: (1) the size of the voice-box, or larynx, and the length of the cords, and (2) the action of the neuro-muscular mechanism whereby the length, approximation, and tension of the vocal cords can be modified when singing from the lowest note to the highest note of the register.
Thus the compass of the—
Bass voice is D to f 75- 354 vibs. per sec.
Tenor " c " c'' 133- 562 " "
Contralto " e " g'' 167- 795 " "
Soprano " b " f''' 239-1417 " "
The complete compass of the human voice therefore ranges from about D 75 to f''' 1417 vibrations per second, but the quality of the same notes varies in different individuals.
Fig. 9
Fig. 9.—Description of the laryngoscope and its mode of use.—The laryngoscope consists of a concave mirror which is fixed on the forehead with a band in such a way that the right eye looks through the hole in the middle. This mirror reflects the light from a lamp placed behind the right side of the patient, who is told to open the mouth and put out the tongue. The observer holds the tongue out gently with a napkin and reflects the light from the mirror on his forehead on to the back of the throat. The small mirror, set at an angle of 45° with the shaft, is of varying size, from half an inch to one inch in diameter, and may be fixed in a handle according to the size required. The mirror is warmed to prevent the moisture of the breath obscuring the image, and it is introduced into the back of the throat in such a manner that the glottis appears reflected in it. The light from the lamp is reflected by the concave mirror on to the small mirror, which, owing to its angle of 45°, illuminates the glottis and reflects the image of the glottis with the vocal cords.
The discovery of the laryngoscope by Garcia enabled him by its means to see the vocal cords in action and how the reed portion of the vocal instrument works (vide [fig. 9] and description). The chink of the [!-- pagenumber --]glottis or the opening between the vocal cords as seen in the mirror of the laryngoscope varies in size. The vocal cords or ligaments appear dead white and contrast with the surrounding pink mucous membrane covering the remaining structures of the larynx. [Fig. 10] shows the appearance of the glottis in respiration and vocalisation. The vocal cords of a man are about seven-twelfths of an inch in length, and those of a boy (before the voice breaks) or of a woman are about five-twelfths of an inch; and there is a corresponding difference in size of the voice-box or larynx. This difference [!-- pagenumber --]in length of the vocal cords accounts for the difference in the pitch of the speaking voice and the register of the singing voice of the two sexes. We should also expect a constant difference in the length of the cords of a tenor and a bass in the male, and of the contralto and soprano in the female, but such is not the case. It is not possible to determine by laryngoscopic examination what is the natural register of an individual's voice. The vocal cords may be as long in the tenor as in the bass; this shows what an important part the resonator plays in the timbre or quality of the voice. Still, it is generally speaking true, that a small larynx is more often associated with a higher pitch of voice than a large larynx.
Fig. 10
Fig. 10.—Diagram (modified from Aikin) illustrating the condition of the vocal cords in respiration, whispering, and phonation. (1) Ordinary breathing; the cords are separated and the windpipe can be seen. (2) Deep inspiration; the cords are widely separated and a greater extent of the windpipe is visible. (3) During the whisper the vocal cords are separated, leaving free vent for air through the glottis; consequently there is no vibration and no sound produced by the cords. (4) The soft vocal note, or aspirate, shows that the chink of the glottis is not completely closed, and especially the rima respiratoria (the space between the vocal processes of the pyramidal cartilages.) (5) Strong vocal note, produced in singing notes of the lower register. (6) Strong vocal note, produced in singing notes of the higher register.
Musical notes are comprised between 27 and 4000 vibrations per second. The extent and limit of the voice may be given as between C 65 vibrations per second and f''' 1417 vibrations per second, but this is most exceptional, it is seldom above c''' 1044 per second. The compass of a well-developed singer is about two to two and a half octaves. The normal pitch, usually called the "diapason normal," is that of a tuning-fork giving 433 vibrations per second. Now what does the laryngoscope teach regarding the change occurring in the vocal cords during the singing of the two to two and a half octaves? If the vocal cords are observed by means of the laryngoscope during phonation, no change is seen, owing to the rapidity of the vibrations, although a scale of an octave may be sung; in the lower notes, however, the vocal cords are seen not so closely approximated as in the very high notes. This may account for the difficulty experienced in singing high notes piano. Sir Felix Semon in a Friday evening lecture at the Royal Institution showed some remarkable photographs, by Dr. French, of the larynx of two great singers, a contralto and a high soprano, during vocalisation, which exhibit changes in the length of the vocal cords and [!-- pagenumber --]in the size of the slit between them. Moreover, the photographs show that the vocal cords at the break from the lower to the upper register exhibit characteristic changes.
Fig. 11
Fig. 11.—Drawings after Dr. French's photographs in Sir Felix Semon's lecture on the Voice, (1) Appearance of vocal cords of contralto singer when singing F# to D; it will be observed that the cords increase in length with the rise of the pitch, presumably the whole cord is vibrating, including the inner strand of the vocal muscle. At the break from D to E (3 and 4) the cords suddenly become shorter and thicker; presumably the inner portion of the vocal muscle (thyro-arytenoid) is contracting strongly, permitting only the edge of the cord to vibrate. For the next octave the cords are stretched longer and longer; this may be explained by the increasing force of contraction of the tensor muscle stretching the cords and the contained muscle, which is also contracted.
When we desire to produce a particular vocal sound, a mental perception of the sound, which is almost instinctive in a person with a musical ear, awakens by association motor centres in the brain that preside over the innervation currents necessary for the approximation and minute alterations in the tensions of the vocal cords requisite for the production of a particular note. We are not conscious of any kinæsthetic (sense of movement) guiding sensations from the laryngeal muscles, but we are of the muscles of the tongue, lips, and jaw in the production of articulate [!-- pagenumber --]sounds. It is remarkable that there are hardly any sensory nerve endings in the vocal cords and muscles of the larynx, consequently it is not surprising to find that the ear is the guiding sense for correct modulation of the loudness and pitch of the speaking as well as the singing voice. In reading music, visual symbols produced by one individual awakens in the mind of another mental auditory perceptions of sound varying in pitch, duration, and loudness. Complex neuro-muscular mechanisms preside over these two functions of the vocal instrument. The instrument is under the control of the will as regards the production of the notes in loudness and duration, but not so as regards pitch; for without the untaught instinctive sense of the mental perception of musical sounds correct intonation cannot be obtained by any effort of the will. The untaught ability of correct appreciation of variations in the pitch of notes and the memorising and producing of the same vocally are termed a musical ear. A gift even to a number of people of poor intelligence, it may or may not be associated with the sense of rhythm, which, as we have seen, is dependent upon the mental perception of successive movements associated with a sound. Both correct modulation and [!-- pagenumber --]rhythm are essential for melody. The sense of hearing is the primary incitation to the voice. This accounts for the fact that children who have learnt to speak, and suffer in early life with ear disease, lose the use of their vocal instrument unless they are trained by lip language and imitation to speak. The remarkable case of Helen Keller, who was born blind and deaf, and yet learned by the tactile motor sensibility of the fingers to feel the vibrations of the vocal organ and translate the perceptions of these vibrations into movements of the lips and tongue necessary for articulation, is one of the most remarkable facts in physiological psychology. Her voice, however, was monotonous, and lacked the modulation in pitch of a musical voice. Music meant little to her but beat and pulsation. She could not sing and she could not play the piano. The fact that Beethoven composed some of his grandest symphonies when stone deaf shows the extraordinary musical faculty he must have preserved to bear in his mind the grand harmonies that he associated with visual symbols. Still, it is impossible that Beethoven, had he been deaf in his early childhood, could ever have developed into the great musical genius that he became.
Fig. 12
Fig. 12.—Diagram showing the position of the larynx in respect to the resonator and tongue. The position of the vocal cords is shown, but really they would not be seen unless one half of the shield cartilage were cut away so as to show the interior of the voice-box. Sound vibrations are represented issuing from the larynx, and here they become modified by the resonator; the throat portion of the resonator is shown continuous with the nasal passages; the mouth portion of the resonator is not in action, owing to the closure of the jaw and lips. The white spaces in the bones of the skull are air sinuses. In such a condition of the resonator, as in humming a tune, the sound waves must issue by the nasal passages, and therefore they acquire a nasal character.