[The macroscopic and microscopic study of the human lateral pterygoid muscle].

The purpose of this investigation was to study the morphology of the human lateral pterygoid muscle and its attachment to the temporomandibular joint. A total of twenty-five lateral pterygoid muscles, twenty for macroscopic and five for microscopic study, were obtained with their temporomandibular joints from eighteen adult cadavers. The results were as follows: 1) The lateral pterygoid muscles observed in this study were classified into three types based on the number of their heads; 65% of the macroscopic specimens had two heads (superior and inferior), 20% three heads (superior, inferior and medial), and 15% a single head. 2) The fascicular architecture of the single-headed specimens was quite simple and so the orientation of their fasciculi was parallel or radial to the line of pull. In their course the fasciculi of the two and three-headed specimens showed a relatively complicated architecture, having a large number of crossover fibers between each head. 3) In all specimens observed macroscopically, the uppermost fasciculi were inserted into the articular disc and capsule of the temporomandibular joint and the rest were inserted into the pterygoid fovea of the neck of the mandible, although no clear boundary could be found between them on their lateral surfaces. The bulk of the fasciculi which were inserted into the articular disc relative to the total amount of the lateral pterygoid muscles was estimated as being in the range of one fifth to one tenth. 4) From the microscopical examination of the specimens the cross-sectional area of the fasciculi which were inserted into the articular disc was about 3 mm2 at their attachment and this corresponded to 30% of the superior head and 3% of total amount of the lateral pterygoid muscle. 5) The fasciculi attached to the articular disc were derived from the superior and medial head of the lateral pterygoid muscle and from the temporalis muscle. In two cases of the twenty examined macroscopically, the fasciculi derived from the inferior head of the lateral pterygoid muscles were inserted into the articular disc.