To investigate the relationship among jaw movements, jaw, tongue, and hyoid muscle activities during chewing and swallowing, and clarify how physical characteristics of foods affect the coordination of these muscle activities, we recorded jaw movement trajectories and muscle activities in the freely behaving rabbit. The phase duration, gape and excursion sizes of jaw movements as well as the duration and peak values of electromyographic burst activities were obtained and compared among three foods (pellet, bread and banana) .<BR>1 . Chewing cycles<BR>During chewing, the opening phase duration was most closely related to the total phase duration, suggesting that the opening phase controlled the masticatory cycle duration. The chewing cycles consisted of three phases (fast closing, slow closing, and opening phases) in pellet and bread chewing, however, only two phases (closing and opening phases) were observed in banana chewing. The muscles recorded can be divided into two groups; one muscle group consists of a jaw-closing muscle [masseter muscle (Mass) ] and a tongue retracting muscle [styloglossus muscle (SG) ], and the other group consisted of a jaw-opening muscle [digastric muscle (Dig) ], a suprahyoid muscle [mylohyoid muscle (MH) ] and a tongue protrusive muscle [genioglossus muscle (GO) ] . The former group appeared to be mainly activated in the jaw-closing phase and the latter in jaw-opening phase, and these patterns were similar among foods. The results suggest that the MH and SG muscles play a critical role in compressing the bolus between the tongue and palate, particularly in banana chewing.<BR>2 . Swallowing cycles<BR>The swallowing cycle was found to have longer cycle duration than that of the chewing cycle as if an extra phase (a pause) occurred in the opening phase. The swallowing cycle consisted of five phases (fast closing, slow closing, opening 1, opening 2, and opening 3 phases) in pellet and bread swallowing, however, only three phases (closing, slow opening and fast opening phases) in banana swallowing. Swallow-related activities that began in the middle of the jaw-closing phase were observed in the GG, MH and SG muscles. The MH and SG muscles were thought to participate in a leading complex activity of tongue movements during swallowing. The MH activity in pellet swallowing had a second peak during the jaw-opening phase, and this suggested that the MH muscle plays a critical role of pulling the laryngeal cartilage and creating a space at the esophagus for food passage.<BR>During swallowing the Dig muscle was active as with the Mass muscle in the jaw-closing phase, this may be due to co-activation of the antagonist (the Mass and Dig) muscles which might stabilize the jaw near the rest position.<BR>We concluded that the mechanism underlying the coordination of the jaw and tongue muscle movements might be maintained not only during chewing but also during swallowing and may be modulated depending on the physical characteristics of foods. Particularly in chewing soft foods like banana, the tongue could play a critical role in compressing and transporting the bolus against the palate during the bucco pharyngeal stage of swallowing and this could lead to modulation of jaw movements as well as muscle activities.