Reidenberg Joy S, Laitman Jeffrey T
Center for Anatomy and Functional Morphology, Mount Sinai School of Medicine, New York, New York 10029, USA.
Anat Rec (Hoboken). 2007 Jun;290(6):745-59. doi: 10.1002/ar.20544.
The mechanism of mysticete (baleen whale) vocalization has remained a mystery. Vocal folds (true vocal "cords"), the structures responsible for sound production in terrestrial mammals, were thought to be absent in whales. This study tests the hypothesis that the mysticete larynx possesses structures homologous to vocal folds and that they are capable of sound generation. Laryngeal anatomy was examined in 37 specimens representing 6 mysticete species. Results indicate the presence of a U-shaped fold (U-fold) in the lumen of the larynx. The U-fold is supported by arytenoid cartilages, controlled by skeletal muscles innervated by the recurrent laryngeal nerve, is adjacent to a diverticulum (laryngeal sac) covered with mucosa innervated by the superior laryngeal nerve, and contains a ligament-conditions that also define the vocal folds of terrestrial mammals and, therefore, supports homology. Unlike the vocal folds of terrestrial mammals, which are perpendicular to airflow, the mysticete U-fold is oriented parallel to airflow. U-fold adduction/abduction and elevation/depression may control airflow, and vibration of its edges may generate sounds. The walls of the laryngeal sac can expand and contract, may serve as a resonant space, and may also propagate vibrations generated by movements of the supporting arytenoid cartilages. The extensive musculature surrounding the laryngeal sac may enable rapid and forceful expulsion of air from the lumen of the sac into other respiratory spaces, or maintain a constant sac volume despite the effects of ambient pressure (e.g., changes during diving or ascent). The size and complexity of the mysticete larynx indicates an organ with multiple functions, including protection during breathing/swallowing, regulation of airflow and pressures in the respiratory spaces, and sound generation. The presence of a vocal fold homolog offers a new insight into both the mechanism of sound generation by mysticetes and the divergent evolution of odontocete and mysticete cetaceans.
须鲸发声的机制一直是个谜。声带（真正的声带“ cords”）是陆生哺乳动物中负责发声的结构，人们认为鲸鱼中不存在这种结构。本研究检验了以下假设：须鲸的喉部拥有与声带同源的结构，并且它们能够发声。对代表6种须鲸物种的37个标本进行了喉部解剖。结果表明，喉部管腔内存在一个U形褶皱（U褶皱）。U褶皱由杓状软骨支撑，由喉返神经支配的骨骼肌控制，与由喉上神经支配的黏膜覆盖的憩室（喉囊）相邻，并且包含一种韧带——这些条件也定义了陆生哺乳动物的声带，因此支持了同源性。与垂直于气流的陆生哺乳动物声带不同，须鲸的U褶皱与气流平行排列。U褶皱的内收/外展和抬高/降低可能控制气流，其边缘的振动可能产生声音。喉囊壁可以扩张和收缩，可能作为一个共振空间，也可能传播由支撑杓状软骨运动产生的振动。围绕喉囊的广泛肌肉组织可能使空气从囊腔快速有力地排出到其他呼吸空间，或者尽管存在环境压力的影响（例如潜水或上升过程中的变化）仍保持囊腔体积恒定。须鲸喉部的大小和复杂性表明这是一个具有多种功能的器官，包括呼吸/吞咽时的保护、呼吸空间中气流和压力的调节以及发声。声带同源物的存在为须鲸发声机制以及齿鲸和须鲸鲸类的趋异进化提供了新的见解。
