Positional relationships between the masticatory muscles and their innervating nerves with special reference to the lateral pterygoid and the midmedial and discotemporal muscle bundles of temporalis

For an accurate assessment of jaw movement, it is crucial to understand the comprehensive formation of the masticatory muscles with special reference to the relationship to the disc of the temporomandibular joint. Detailed di ssection was performed on 26 head halves of 14 Japanese cadavers in order t o obtain precise anatomical information of the positional relationships bet ween the masticatory muscles and the branches of the mandibular nerve. Afte r complete removal of the bony elements, the midmedial muscle bundle in all specimens and the discotemporal muscle bundle in 6 specimens, derivatives of the temporalis, which insert into the disc were observed. On the anterio r area of the articular capsule and the disc of the temporomandibular joint , the upper head of the lateral pterygoid, the midmedial muscle bundle of t emporalis and the discotemporal bundle of temporalis were attached mediolat erally, and in 3 specimens the posterosuperior margin of the zygotnaticoman dibularis was attached to the anterolateral area of the disc. It is suggest ed that these muscles and muscle bundles contribute to various mandibular m ovements. Although various patterns of the positional relationships between the muscles and muscle bundles and the their innervating nerves are observ ed in the present study, relative positional relationships of the muscles a nd muscle bundles and of nerves of the mandibular nerve are consistent. A p ossible scheme of the developmental formation of the masticatory muscles ba sed on the findings of the positional relationships between the muscles and the nerves is presented.