Lateral pterygoid: two muscles?

Reinterpretation of existing data and introduction of new evidence appear to indicate that this controversial muscle might better be treated as two muscles. Anatomically the lateral pterygoid in man and in the rhesus macaque has two distinct heads, superior and inferior. Biomechanically, the two heads posses different properties: the superior head has a closing moment (or perhaps no moment) while the inferior head has an opening moment. The findings are similar in the two species. Electromyographically the two heads show different activity patterns: the superior head is active during various jaw-closing movements only, while the inferior head is active during jaw-opening and protrusion only. Functionally, therefore, the lateral pterygoid of man and rhesus macaque appears to be two muscles.

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