Oblique Thyroarytenoid Muscle in Humans: An Independent Muscle or an Accessory Belly?

Objectives/Hypothesis: This study aimed to determine the prevalence and morphological variations of the oblique thyroarytenoid (TA) muscle in humans. Study Design: Cadaveric anatomic dissections. Methods: One hundred hemilarynges from 50 formalin-embalmed cadavers were dissected to investigate the morphology of muscle fibers of the TA muscle. Results: Thirty-six (36%) hemilarynges were found to have a distinct oblique belly superficial to the TA muscle. In 28 cases, the belly had a relatively constant origin and an insertion that extended straight onto the TA muscle from the anterosuperior area of the internal surface of the thyroid lamina to the base of the muscular process of the arytenoid cartilage. Eight cases were located in a similar area but with some differences in the origin or insertion features. Conclusions: We proposed that the oblique TA muscle has a high prevalence and probably acts to close and relax the vocal cords. It remains to be determined whether the oblique TA muscle is an independent muscle or an accessory belly of the main TA muscle.