While several muscles contribute to chewing (mastication), only one is primarily responsible for opening the jaw: the lateral pterygoid. This muscle, located on the side of the head, originates from the sphenoid bone and inserts into the mandible. Its contraction pulls the mandible forward and downward, causing the mouth to open. Understanding the role of the lateral pterygoid is crucial in diagnosing and treating temporomandibular joint (TMJ) disorders.