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 dissection was performed on 26 head halves of 14 Japanese cadavers in order to obtain precise anatomical information of the positional relationships between the masticatory muscles and the branches of the mandibular nerve. After 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 anterior area of the articular capsule and the disc of the temporomandibular joint, the upper head of the lateral pterygoid, the midmedial muscle bundle of temporalis and the discotemporal bundle of temporalis were attached mediolaterally, and in 3 specimens the posterosuperior margin of the zygomaticomandibularis was attached to the anterolateral area of the disc. It is suggested that these muscles and muscle bundles contribute to various mandibular movements. Although various patterns of the positional relationships between the muscles and muscle bundles and the their innervating nerves are observed in the present study, relative positional relationships of the muscles and muscle bundles and of nerves of the mandibular nerve are consistent. A possible scheme of the developmental formation of the masticatory muscles based on the findings of the positional relationships between the muscles and the nerves is presented.

It was emphasized that the nerve originating from SMPlx to the uncinate process chiefly ran along the IPDA and it was necessary to focus one's attention not only on the extrapancreatic perineural invasion but also on the intrapancreatic perineural invasion in carcinoma of the body and tail of the pancreas.

Detailed examinations were performed in ten temporal muscles from five cadavers to identify the muscle bundle arrangements of the temporalis and their innervation. Three additional muscle bundles were clearly observed in the main part of the fan-shaped temporalis: the anteromedial, anterolateral, and mid-lateral muscle bundles. Based on the origins, insertions and detailed innervation patterns, these bundles were considered as parts of the temporalis rather than independent muscles, although the anteromedial and anterolateral bundles had been recently reported as newly described muscles. A possible schematic model of the origins of these muscle bundles is proposed. We also report a branch from the posterior deep temporal nerve which was distributed to the temporal fascia and to the skin of the temporal region.

The soft palate is considered to be located in the border region between the areas of distribution of the lesser palatine nerve and pharyngeal plexus. This may be why controversies exist in previous studies about the innervation of the soft palate muscles.

Summary: For an accurate assessment of jaw movement, it is critical to understand the comprehensive formation of the masseter. Detailed dissection was performed on fifteen head halves of eight Japanese cadavers in order to obtain precise anatomical information of the course and distribution of the masseteric nerve in the masseter, especially in the zygomaticomandibularis (ZM). Based on detailed innervation investigation, the main trunk of the masseteric nerve ran between ZM and the masseter, and the anterior region of ZM was closely related to the lateral layer of the masseter rather than the medial layer. Considering the positional relationships between the muscles and the innervating branches, it might be proposed that the muscle masses of ZM and the masseter migrate from the posterior side of the temporalis anterolateralward during development. This model is in agreement with the findings in that no nerve branch was observed between the temporalis and ZM.