Innervation analysis of the small muscle bundles attached to the temporalis: truly new muscles or merely derivatives of the temporalis?

Abstract

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.

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.…”

“…The anterolateral and anteromedial muscle bundles of temporalis were observed as described by Shimokawa et al (1998). On the broad fan-shaped main part of temporalis, the anterolateral temporalis bundle was located on the lateral surface of the aponeurosis of the main part of the muscle.…”

“…The midlateral bundle which is located on the lateral surface of the middle region of the muscle has been reported as the lateral muscle bundle of temporalis (Eisler, 1912) and the superficial temporalis (Yoshikawa & Suzuki, 1962). Shimokawa et al (1998), based on an innervation investigation, proposed that these 3 bundles are considered as parts of temporalis rather than as independent muscles, and simply called these bundles the anteromedial, anterolateral and midlateral muscle bundles of temporalis. In addition, a bundle (discotemporal bundle) from the posterior part of temporalis which attaches to the lateral third of the disc has been reported (Couly et al 1975(Couly et al a, b, 1976Couly, 1980 ;Le Toux et al 1989 ;Naohara, 1989 ;Merida Velasco et al 1993).…”

“…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.…”

“…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. The anteromedial muscle bundle may be derived from the anteriormost part of the anlage of temporalis, and may move to the medial surface of the main part of temporalis (Shimokawa et al 1998).…”