An anatomic study of the divisions of the lateral pterygoid muscle based on the findings of the origins and insertions.

The lateral pterygoid muscle has been generally described as a muscle composed of two separate heads, however, the border between these heads has not clearly identified. In the present study, we investigated the positional relationships between the muscle and the surrounding nerves, and examined the muscle bundle arrangements to determine the detailed information of the origins and insertions. We used 94 specimens of 52 Japanese cadavers (29 males and 25 females) for the investigations of the nerve courses, and randomly chose and used 10 specimens of 5 (2 males and 3 females) cadavers from above-mentioned 52 cadavers for the detailed examinations of the muscle fiber constructions. In some specimens, the buccal nerve passed through the gap in the muscle, however, in many cases the nerve pierced the muscle. The muscle inserted into the medial half of the anterior surface and the medial surface of the condylar process. Only a thin superficial layer of the muscle fibers was attached to the inferior surface of the articular disc. According to the positions of the origins and insertions of the muscle and the positional relationships to the nerves, the muscle was not clearly divided into heads. The detailed findings of the origins and insertions of the present study suggest that the muscle is a single muscle with no clear border, containing fibers of various directions. A two-head muscle pattern would be indicated by the differences of the convergences of the muscle fibers.