Which of the following muscles assists in side-to-side jaw movement?

The lateral pterygoid is the muscle that plays a crucial role in side-to-side jaw movements, also known as lateral excursion. This muscle is one of the key muscles involved in the complex motion of the jaw, specifically in facilitating the grinding action necessary for chewing.

When the lateral pterygoid contracts, it helps to move the jaw forward and to the side, allowing for effective mastication, especially when breaking down food. The muscle's position and orientation enable it to pull the head of the mandible forward and laterally, which is essential for the proper function of the temporomandibular joint (TMJ).

Other muscles mentioned, such as the buccinator and orbicularis oris, serve different purposes related to facial expression and manipulating food within the mouth but do not contribute to the side-to-side motion of the jaw. The temporalis muscle, while it plays a significant role in elevating the mandible, primarily facilitates vertical movements rather than lateral adjustments. Therefore, when considering the muscles involved specifically in lateral jaw movement, the lateral pterygoid is the clear choice.