The Mechanism of the Larynx Part I: The Movements of the Arytenoid and Cricoid Cartilages

An analysis of a radiographic study of the movements of the arytenoid and cricoid cartilages has been correlated with anatomical findings. The results show the usual description of the movements of the arytenoids is not entirely correct. When the glottis is open there is very little narrowing of the airway: the vocal folds are turned upwards into the laryngeal ventricles and the arytenoid cartilages rest on the upper and lateral aspects of the cricoarytenoid facets, inclined about 45 deg. outwards. When the glottis is closed the arytenoids are moved downwards and forwards on the cricoarytenoid facets and rocked over medially through an arc of about 40 deg. until the arytneoid masses are opposed: by this means the vocal processes to which are attached the triangular vocal folds are moved downwards and medially, the vocal processes describing an arc of about 40 deg. downwards. The cricothyroid movements serve to move the arytenoids bodily. The essential component is an upward elevation of the anterior rim of the cricoid towards the thyroid in a visor-like action. Closure of the cricothyroid visor results in elongation of the vocal folds and is seen best in the production of high-pitched sound; the visor is partly opened at rest and may be opened farther during swallowing or abdominal straining or any other act in which the larynx closes. Combinations of the cricoarytenoid and cricothyroid movements make possible a wide range of adjustments in the length, depth and tension of the vocal cords. The significance of these findings in the field of clinical medicine is discussed and an account is given of patients who show absence of cricothyroid movements.