The Mechanism of the Larynx—II The epiglottis and closure of the larynx

An anatomical, clinical and radiological study has been made of the mechanism of closure of the larynx. In swallowing there are some five components. (1) Elevation of the larynx to the hyoid bone and of the larynx and hyoid towards the lower jaw which results in backward tilting of the leaf of the epiglottis. (2) Downward, forward and inward rocking movement of the arytenoid cartilages which closes the glottis and narrows the vestibule. (3) Opening of the crico-thyroid visor which allows the arytenoids to tilt bodily farther forward. (4) Bulging backwards of the vestibular portion of the epiglottis, due to thyro-hyoid approximation acting through the medium of compression of the hyo-thyroid fat pad, allows the vestibular folds to be approximated and the cavity of the vestibule to be obliterated. (5) Downward turning of the leaf of the epiglottis. The leaf is tilted backwards by thyro-hyoid approximation with the larynx and hyoid bone elevated to the lower jaw; from this position the leaf is downward turned by pressure exerted through the bolus and is pressed against the larynx by the pharyngeal constrictor wave. These five components are normally closely integrated, but may be partially or wholly dissociated in unusual or abnormal circumstances. The larynx may also be closed partially or completely for many other reasons, including breath-holding, abdominal straining, and phonating. In all these circumstances the basic components of the mechanism employed are the same as for swallowing, except for the fact that the epiglottis is not turned down. All these components are used with different degrees and combinations to vary size, form and alignment of the laryngeal lumen in speech. The hyoid bone is also an important structure. Apposition of the thyroid cartilage to the hyoid bone is an essential component of laryngeal closure. By this means there may be introduced many variations in the shape and alignment of the laryngeal vestibule and vestibular folds, which must have considerable influence on function. The role of this mechanism in voice production has been largely overlooked. The formation of the laryngeal ventricles and the changes in form and size of the vestibular folds are also described; it is considered that these influence the effective length of the vocal folds.