It is scarcely possible, however, that the larynx literally remains unchanged through the period of the child’s life, extending from the age of six to fourteen or fifteen years. In point of fact, authorities upon the subject refer only to the lack of growth and development in size of the larynx during the period; but undoubtedly, during these years, there is a constant gaining of firmness and strength, in both the cartilages and their connecting membranes and muscles. None of the books written upon the voice have even mentioned this most important fact. It bears with great significance upon questions relating to the capacities of the child’s voice at different ages, and explains that phenomenon called the “movable break,” which has puzzled so many in their investigations of the registers of the child’s voice. The constant, though of course extremely slow, hardening of the cartilaginous portions of the larynx, and the steady increase in the strength of its muscles and ligaments is not in the least inconsistent with the previously noted fact, that the vocal bands during this time increase to no appreciable extent in length; for, it may be observed, after the change of voice, which often occurs with great rapidity, and during which the vocal bands increase to double their previous length in males, that, though the pitch of the voice, owing to increased length of the bands, suddenly lowers, yet not until full maturity is reached, do the laryngeal cartilages attain that rigidity, or the vocal bands that ready elasticity essential to the production of pure, resonant voice. Yet, during these years, while the voice is developing, the vocal bands remain unchanged in length. Even in those cases where the voice changes slowly in consequence of the slow growth in length and thickness of the vocal cords, it takes several years, after laryngeal development has ceased, for the voice to attain its full size and resonance.
Furthermore, the continual increase in strength and firmness of the larynx from six years onward to puberty, is consistent with the constant growth in strength and firmness of tissue characterizing the entire body. It is again proven by the continual improvement in the power and timbre of the tone through this period, always premising, be it understood, that the voice is used properly, and never forced beyond its natural capabilities. The voice, at the age of eleven or twelve, is far stronger, and is capable of more sustained effort than at the age of six or seven years, and, for the year or two preceding the break of voice, the brilliance and power of boys’ voices, especially in the higher tones, is often phenomenal, and in all cases is far superior to that of previous years.
The resemblance between the voices of boys and girls, a resemblance which amounts to identity, save that the voices of boys are stronger and more brilliant in quality, disappears at puberty.
Among the physical changes which occur at this period is a marked growth of the larynx, sufficient to alter entirely the pitch and character of the boy’s voice. As a female larynx is affected to a lesser extent, the voices of girls undergo little change in pitch, but become eventually more powerful, and richer in tone.
This break of the voice, as it is called, occurs at about the age of fifteen years in this climate, but often a year or two earlier, and not infrequently a year or two later. The growth of the larynx goes on, with greater or less rapidity, varying in different individuals, for from six months to two or three years, until it attains its final size. In boys, the larynx doubles in size, and the vocal bands increase in the proportion of five to ten in length. This great gain in the length of the vocal cords is due to the lateral development of the larynx, for the male larynx, in its entirety, increases more in depth than in height. The result is a drop of an octave in the average boy’s voice, the longer bands producing lower tones. The change in size in the female larynx is in the proportion of five to seven, and the increase is in height instead of depth or width as in the male larynx. The vocal cords of women are, therefore, shorter, thinner and narrower than are those of men.
The reason assigned for the peculiar antics of the boy’s voice, during the break, is unequal rapidity in the growth and development of the cartilages and of the muscles of the larynx. The muscles develop more slowly than do the cartilages, and so abnormal physical conditions produce abnormal results in phonation.
No further changes occur in the laryngeal structure until middle life, when ossification of the cartilages commences. The thyroid is first affected, then the cricoid, and the arytenoids much later.
The consequent rigidity of the larynx occasions diminished compass of the singing-voice, the notes of the upper register being the first to disappear. In some few cases of arrested development, the voice of the man retains the soprano compass of the boy through life.