Final answer:
The muscle extending from the shoulder to the mouth that is involved in facial treatments is the platysma, though the reference does not name it explicitly. The information focuses on the buccinator and muscles involved in mastication, orbicularis oris and oculi, and the occipitofrontalis connected by the epicranial aponeurosis, all contributing to facial expressions.
Step-by-step explanation:
The muscle from the upper part of the shoulder to the corner of the mouth that may be massaged during a facial is the platysma. However, the provided reference information does not explicitly name this muscle, focusing instead on other facial muscles such as the buccinator muscle, which compresses the cheek, and the mastication muscles like the masseter.
The muscles of facial expression are unique because they often insert into the skin rather than onto the bones, allowing for the wide range of facial expressions humans can make. For example, the orbicularis oris is a circular muscle that moves the lips, and the orbicularis oculi is another circular muscle that closes the eye. The occipitofrontalis muscle, with its frontal belly, assists in moving the scalp and eyebrows, and the two bellies are connected by a broad tendon referred to as the epicranial aponeurosis or galea aponeurosis. These muscles, among others detailed in the discussion like the corrugator supercilii, allow for nuanced facial expressions.