The Primate Larynx: A Comparative Physiological Study of Intrinsic Muscles

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Abstract
A study was made of the mechanical properties of the thyroarytenoid and cricothyroid muscles in three primates: Squirrel monkey, rhesus Macaque, and Hynan gibbon. The thyroarytenoid and cricothyroid muscles were stimulated electrically through their respective motor nerve supply. Isometric contractions of muscles were recoded by a force transducer and high-speed inkwriter. Measurements were made of the contraction time, half-relaxation time, tetanus, and tetanus : twitch tension ratio of each muscle. It was found that the thyroarytenoid possessed the properties of a “very fast” muscle (14 msec) and the cricothyroid of the gibbon and rhesus those of a muscle of “average” speed (38 msec). With the exception of the cricothyroid muscle in the squirrel monkey (19 msec), there were no real differences among the three primates studied. Comparative values of both laryngeal muscles were similar for the domestic dog and primate but not for the cat, whose laryngeal muscles had been found to be physically slower. The physiological similarity of the dog and the primate larynx substantiates the dog's value as an experimental analogue for studies in muscle physiology of the larynx.