The authors studied the lateral pterygoid muscle of 179 fresh cadavers by both anatomical dissection and magnetic resonance imaging. The aim was to define the general morphology and the architectural organisation of the lateral pterygoid muscle. Dissection plane by plane, anatomical sections in different planes of space and dissections via multiple approaches on harvested blocks allowed the demonstration that the lateral pterygoid shows an architectural arrangement different from that which is usually described but similar to that, from its typically penniform structure of the masseter and the medial pterygoid. The anatomical situation of this muscle gives rise to numerous differences in opinion much to its morphology as to its functional examination. This study has shown that one part of the muscle has a typical penniform structure made up of alternating musculo-aponeurotic layers and by the absence of individual muscle bellies. In addition the particular shape of this muscle makes it useless to insert intramuscular electrodes in its only accessible portion, which makes the results of electromyographic studies debatable.

Abstract: The authors carried out an anatomical and magnetic resonance imaging study on the architecture of the mandibular elevator muscles of 169 cadavers. The aim of the study was to define the organisational architecture of the human masseter, temporal and pterygoid muscles. Layer by layer dissection and anatomical cuts in different spatial planes showed that the temporal muscle has a different architecture to the other mandibular elevator muscles. Indeed this muscle does not have the pennate structure of the masseter and pterygoid muscles. Through electromyographic study the behavior of this muscle allowed the establishment of its functional segmentation during the masticatory cycle. Our study showed three distinct anatomical portions in the middle of the temporal muscle which correspond to this functional classification. The MRI study confirmed the results of our anatomical study.

The muscle fiber fascicles of the temporo-masseter complex of the cat were minutely dissected. Some heads were embedded in paraffin while others were put into methyl-methacrylate resin and sections were made. The results of this anatomical study demonstrate that this complex consists of the masseter muscle, the temporal muscle and two well individualized transitional fascicles: the maxillomandibularis and zygomato-comandibularis muscles. The masseter and temporal muscles are composed of individualized compartments in which the orientation and aponeuroses of the fibers of which they are composed differ with regard to the centric occlusion plane. The masseter muscle consists of a superficial fascicle made up of two layers, an intermediate fascicle, and a deep fascicle composed of two layers. The temporal muscle consists of one anterior orbital part and one posterior temporal part. This structure is in accordance with the mammalian archetype described by Gaspard and Saban. These findings should lead towards a homology-based nomenclature founded on comparative anatomy studies of mammalian species. Such a classification would permit the comparison of results obtained from physiological and histochemical studies of these complex muscle fibers when they are published by different researchers.

The fleshy bundles of the first lamina of the cat (Felis catus L.) superficial masseter were highly developed, wraping the mandibular angle and rejoining the bundles of the medial pterygoid on the internal face of the mandible. This periangular masseteric-pterigoid girth was subdivided into jaw bone inserted bundles and bundles with free attachment which were opposed through the meato-angular ligament and the masseteric-pterygoid raphe. However, exchanges between the masseteric and pterygoid bundles were never observed. On a functional basis, the periangluar girth is of great importance.

The architectural analysis of the ptérygoidal plane of the cat identified the two pterygoid muscles. The medial pterygoid showed an orbital and an angular part inserted respectively on the internal face of the mandibule and on the maeto-angular ligament. The lateral pterygoid consisted of only one pterygoid bundle, involved in lateral movements and adjustments of the jaw condyle.