An Anatomical Study of the Muscles Innervated by the Masseteric Nerve

Abstract

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.

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

“…The aim of the present study was to examine (1) the discotemporal and the midmedial bundles of temporalis, (2) the ramification of nerves distributed to the lateral pterygoid and temporalis, (3) the positional relationship between the masticatory nerves and the lateral pterygoid muscle, and (4) the intramuscular distribution of the nerves of these muscles. A possible scheme to account for the positional relationships between the masticatory muscles and the branches of the mandibular nerve based on the present findings and our recent studies (Shimokawa et al 1998(Shimokawa et al , 1999 is proposed.…”

“…Therefore, the mandibular nerve trunk may not serve as a clear demarcation between the medial and lateral anlagen. Based Shimokawa et al (1998), and that of zygomaticomandibularis and masseter by Shimokawa et al (1999). Based on the findings of the innervation patterns and the positional relationships between the muscles and nerves, the origins of the masticatory muscles are considered as follows.…”

“…Masseter and zygomaticomandibularis arise from the posterior part of the anlage of the masticatory muscles (Edgeworth, 1914). Shimokawa et al (1999) suggested that during migration the muscle bundle medial to the masseteric nerve trunk might form zygomaticomandibularis, and the muscle bundle lateral to the trunk might form masseter. In addition, it is considered that some muscle bundles are the derivatives of temporalis, and Shimokawa et al (1998) described the anteromedial, anterolateral and midlateral muscle bundles as parts of temporalis.…”

En Bloc Removal of the Mandible, the Trigeminal Muscles and the Mandibular Nerve in Humans

“…Following Tomo's [9] rational reclassification of the masticatory (and related) muscles, Shimokawa and his associates [11,12] and Akita and his coworkers [13,14] undertook a major revision of the subparts of the masseter, the temporalis and lateral pterygoid muscles based on their nerve supply. The major aims of these investigations included: 1) an objective reclassification of these "complicated masticatory muscles" [15]; Tomo et al [10] referred to the temporalis and the masseter each as "muscles"]; 2) to establish the true affinities of muscle slips such as the zygomatico-mandibularis, the pterygoid proprius (Henle), etc.…”

Lamination of the Masticatory Muscles in the Phascolarctos cinereus (Koala) According to Their Innervations

“…In fact, nerves distributed into muscle bundles from other muscle layers often penetrate tendons or aponeuroses (Koppe et al, 1988;Schumacher et al, 1974;Lau et al, 1974;Widmer, 1997). Some researchers have noted specific nerve distributions within these muscles (Akita et al, 2000;Nakajima, 2001;Nakajima et al, 1998Nakajima et al, , 2000Shimokawa et al, 1988Shimokawa et al, , 1999Tomo, 1990;Tomo et al, 1993;Watanabe, 1997). Nerves control the action of muscles, so improved understanding about innervation patterns in the masticatory muscles is important in the consideration of muscle function.…”