A patient sustains a complete fracture through the ramus of the mandible. Which muscle's action would most likely displace the proximal mandibular fragment superiorly?

The masseter muscle attaches from the zygomatic arch to the lateral surface of the ramus and angle of the mandible. When the ramus is fractured, the masseter (along with the medial pterygoid and temporalis) tends to pull the proximal (condylar) fragment superiorly and medially. In ramus fractures, the displacement of fragments is determined by the muscle attachments: the masseter and medial pterygoid (mandibular sling) elevate the proximal fragment, while the digastric, geniohyoid, and mylohyoid muscles pull the distal fragment inferiorly and posteriorly. The temporalis also elevates and retracts, but the masseter is most commonly cited for its dominant role in fragment displacement in ramus fractures.