The anatomy of the larynx of the bowhead whale, Balaena mysticetus, and its sound-producing functions.

This study describes the morphology of the laryngeal apparatus in bowhead whales (Balaena mysticetus) with respect to respiration, deglutition, and vocalization. We also examined the intrinsic cricoarytenothyroid muscle (Musculus (M.) diverticuli laryngei) which forms the laryngeal diverticulum, to ascertain its interactions with the laryngeal cartilages during respiration and sound production. Five fetal larynges and four from adult whales were studied using noninvasive imaging, as well as macroscopic and microscopic techniques. The larynx extends from the skull base into the thoracic inlet. The dorsally curved laryngeal stalk, supported by epiglottis and the corniculate processes of arytenoid cartilages, is situated within the nasopharynx. The epiglottic cartilage exhibits a prominent medial ridge. The arytenoid cartilages are rod-shaped, and extend through the laryngeal cavity. The thyroid cartilage possesses a prominent caudal horn with a fibrous articulation to the ventrally incomplete cricoid cartilage. The M. thyroepiglotticus forms the connection between epiglottic and thyroid cartilages. The M. cricothyroideus lateralis connects the caudal horn of the thyroid cartilage with the cricoid cartilage and the M. cricothyroideus medialis connects the cricoid and thyroid cartilage. An extensive laryngeal diverticulum (Diverticulum laryngis), formed by the laryngeal mucosa and M. diverticuli laryngei, is positioned caudo-ventral to the laryngeal vestibule. The mucosa thickens into a fold medial to the vocal processes of the arytenoid cartilages. Experiments with airflow combined with histological and anatomical evidence strongly suggest a sound producing function for these (vocal) folds. This analysis provides the first account of sound producing structures and function in bowhead whales.