[Analysis of the image of external pterygoid muscle during close and wide open of the jaw by condylo-pterygo-maxillo-oblique projection in magnetic resonance].

External pterygoid muscle is an important muscle. It is easy to be hurt by acute and chronic trauma which may become one of the chief cause of TMJDS. It is difficult to be studied, because it locates deeply. It is covered by thick soft and hard tissues. That is why the questions about its anatomy and physiological functions have been debated. In this paper, the changes of images form of external pterygoid muscle during the jaw closing and wide opening were observed and analysed in 14 cases, 25 sides, of adult men and women. By CPMOP in MR. The results can by concluded that (1) the upper head of this muscle inserts fully or mainly to the condyle pterygoid fossa; (2) the direction of the muscle fibers is not entirely horizontal but with some inclined and (3) the two heads of this muscle are relaxed in the jaw closing and are contracted in the jaw wide opening synchronously.