Abstract
The hyoid bone shows complicated movement during swallowing and speaking. Although the stylohyoid muscle pulls the hyoid bone upward and backward, the structure of the muscle attachment has not been elucidated. As for the stylohyoid muscle, it was clarified using SEM that it is widely attached to the bottom of the corpus of the hyoid bone except for the central portion. In this adhesion portion, a mass of fibrocartilage, 0.5 to 1mm thick and 10 to 17mm long, was recognized along the base of the corpus of the hyoid bone. Before insertion into the fibrocartilage, the tendon fibers of the stylohyoid muscle are involved with other tendon fibers. The same involvement was also recognized in the mass of fibrocartilage. This complication was thought to indicate that muscles were mutually strengthened by combination. It is considered that many muscles are attached to the mass of fibrocartilage, and are useful in changing the position of the hyoid bone, which is supported by many muscles. During swallowing, the hyoid bone also rotates. It is suggested that many muscles inserted in this fibrocartilage facilitate fixation of the hyoid bone. Therefore, it is considered that this fibrocartilage becomes the axis of the rotatory movement. The rotatory movement in the front-back direction was thought to be carried out by the geniohyoid muscle and thyrohyoid muscle.
