[An electromyographic study of the exposed lateral pterygoid muscle in monkey]

The purpose of the present study is to observe the electromyogram (EGM) manifestations of the lateral pterygoid muscle (LPM) in monkey during mouth opening and closing movements. The lateral pterygoid muscle of five healthy monkeys (macaques) was exposed by operation under general anesthsia and the electropolar needles were placed into the superior and inferior head of LPM respectively. The EMG manifestations of the superior and inferior head of LPM were recorded by O.T.E. Biomedica EMG Recorder during the natural condition and the movements of opening and closing mouth after complete recovery from anesthesia. It has been found that the two heads acted synergistically only in opening movement and no activity was noted in closing movement. This finding disagrees with the previous viewpoint that the function of the superior and inferior head of LPM is independent.