Thanks Jules!
I found a very concise explanation about the masseter and likely problem for many with the jaw/ear pain:
The masseter muscle is a facial muscle that plays a major role in the chewing of solid foods. The muscle is shaped similar to a parallelogram, connecting to the mandible (lower jawbone) and the cheekbone.
The masseter is divided into two distinct sections, the ‘superficial’ and ‘deep’ portions. The superficial portion of the masseter is the thick and tendon-like portion of the muscle that connects to the cheekbone, while the deep portion is the smaller and more muscular portion of the muscle that connects to the mandible.
During chewing, the masseter is assisted by three other muscles: the temporalis, medial pterygoid, and lateral pterygoid. The four muscles work together to pull the jaw down and back up again. The masseter is the key muscle that pulls the mandible upward. All four muscles are connected to a single division of the trigeminal nerve.